Performance of HSPA and Mobile WiMAX

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  • 1. white paper 284 23-3128 Uen Rev B | June 2009 Technical overview and performance of HSPA and Mobile WiMAX How the performance of HSPA and Mobile WiMAX compare, in theory and in practice.
  • 2. Contents 1 Introduction 3 1.1 HSPA 4 1.2 Mobile WiMAX 5 2 Technical comparison 7 2.1 Similarities 7 2.2 Differences 11 2.3 Summary technical comparison 14 3 Performance characteristics 14 3.1 Peak data rates 15 3.2 Spectrum efficiency 16 3.3 Coverage 17 3.4 Real-life experience 19 4 Network architecture 21 4.1 WiMAX Forum and IEEE 22 4.2 Architecture comparison 23 4.3 System architecture evolution 24 4.4 Mobile WiMAX 24 5 Conclusion 25 6 Glossary 26 7 References 27 2 Technical overview and performance of HSPA and Mobile WiMAX Contents
  • 3. 1 Introduction The internet has had a dramatic impact on transmitter and receiver, effectively our private and professional lives. And its multiplying the peak rate importance continues to grow. To fully enjoy ✒ for improved QoS and low latency the benefits of the internet, however, users • dynamic scheduling, with end-user need a broadband connection. In coming traffic streams prioritized according to years, millions of people will turn to wireless service agreements technology for this experience. • short transmission time intervals (TTI), A host of technologies are competing to allowing round-trip times to approach deliver commercial mobile broadband that of wired equivalents (such as DSL) services. By far the most successful of these ✒ for higher capacity is high-speed packet access (HSPA), which • shared-channel transmission to make has been commercially deployed by over 250 efficient use of available time/ operators in more than 110 countries.1 HSPA frequency/codes and power resources is a state-of-the-art technology that can • link adaptation to dynamically optimize provide mobile and wireless broadband transmission parameters, depending on services with unsurpassed performance and actual radio conditions economies of scale to the vast majority of the • channel-dependent scheduling to market. By 2010, when it is anticipated that assign radio resources to users with the number of wireless broadband the most favorable radio conditions connections will exceed 600 million, HSPA • hybrid automatic repeat request will deliver more than 70 percent of all mobile (HARQ) to enable rapid retransmission broadband connections. of missing data, and soft-combining A good mobile broadband system must to significantly improve performance fulfill certain criteria, including high data rate, and robustness high capacity, low cost per bit, low latency, ✒ for greater coverage good quality of service (QoS), and good • advanced antenna systems and coverage. Several techniques can be receivers to enhance the radio link and used to meet these criteria in a wireless improve cell range. system, including: Both HSPA and Mobile WiMAX employ ✒ for higher data rates (and capacity) most of these techniques, and their • higher-order modulation schemes, such performance is broadly similar. However, they as 16 and 64 quadrature amplitude differ in areas such as the duplex scheme modulation (16QAM and 64QAM) (FDD versus TDD), frequency bands, multiple • multiple-input, multiple-output (MIMO) access technology, and control channel advanced antenna systems that rely on design, giving rise to differences mainly in multiple antennas at both the uplink data rates and coverage. 1 Source: Global mobile Suppliers Association (GSA), March 2009 Technical overview and performance of HSPA and Mobile WiMAX Introduction 3
  • 4. 1.1 HSPA The Third Generation Partnership Project 14Mbps. These enhancements, which (3GPP) is a collaboration that brings together commonly go under the denomination several telecommunications standards bodies HSDPA (high-speed downlink packet access), in the USA, Europe, Japan, South Korea and were a first step in the evolution of WCDMA. China. At present, 3GPP has more than 400 Although a great deal of traffic is downlink- member companies and institutions. The oriented, several applications also benefit 3GPP defines GSM and WCDMA from an improved uplink. Examples include specifications for a complete mobile system, the sending of large e-mail attachments, including terminal aspects, radio access pictures, video clips and blogs. The key networks, core networks, and parts of the enhancement in WCDMA 3GPP Release 6 service network. Standardization bodies in was a new transport channel in the uplink: each world region have a mandate to take enhanced uplink (EUL), also sometimes output from the 3GPP and publish it in their called HSUPA (high-speed uplink packet region as formal standards. access). This enhancement improved 3GPP specifications are structured in throughput, reduced latency and increased releases. Ordinarily, discussions of 3GPP capacity. EUL provides data rates of up technologies refer to the functionality in one to 5.8Mbps. or another release. It is worth noting that all The combination of HSDPA and EUL is new releases are backward-compatible with called HSPA. To further boost the peak data previous releases. rate and capacity, 3GPP Release 7 The development of the 3GPP technology introduced HSPA evolution (also called track (GSM/WCDMA/HSPA) has been HSPA+), which supports MIMO, 64QAM in spectacular. Over a period of 10 years, for the downlink, and 16QAM in the uplink. Rel 8 example, there has been a 1,000-fold support 2 ways to give downlink bitrates of increase in supported data rates. Moreover, 42Mbps, one is the combination of 64QAM the 3GPP technologies continue to evolve. and MIMO and the other way is by using dual WCDMA 3GPP Release 99 provided data carriers with 64QAM modulation. rates of 384Kbps for wide-area coverage. In future releases we will see both Greater speed (data rates) and capacity combinations of dual carriers and MIMO were soon required, however, (at lower and combinations of up to 4 carriers, both production cost) as new services were these alternatives support up to 84Mbps introduced and more people began to use and even higher bitrates are possible if packet data services. combinations of MIMO and 4 carriers will Among other things, WCDMA 3GPP be supported in the future. Release 5 extended the specification with a Long-term evolution (LTE), also specified in new downlink transport channel, the high- 3GPP Release 8, introduces OFDM/OFDMA speed downlink shared channel, which technology in the downlink and single-carrier enhanced support for high-performance FDMA (SC-FDMA) in the uplink. LTE supports packet-data applications. Compared with very high data rates – more than 300Mbps in Release 99, the enhanced downlink gave a the downlink and 80Mbps in the uplink. In considerable increase in capacity, which addition, it supports operation both in paired translated into reduced production cost per and unpaired spectrum (FDD and TDD) using bit. It also significantly reduced latency and channel bandwidths of approximately 1.4MHz provided downlink data rates of up to up to 20MHz. 4 Technical overview and performance of HSPA and Mobile WiMAX Introduction
  • 5. Table 1: Progressive enhancements to 3GPP specifications Version Released Info Release 99 2000 Q1 Specified the first UMTS 3G networks, incorporating a WCDMA air interface Release 4 2001 Q2 Added features, including an all-IP core network Release 5 2002 Q1 Added IMS and HSDPA Release 6 2004 Q4 Integrated operation with Wireless LAN networks, added enhanced uplink, MBMS and enhancements to IMS such as Push to Talk over Cellular (PoC) Release 7 2007 Q4 Added downlink MIMO, reduced latency, improved QoS and improvements to real-time applications like VoIP Release 8 2009 Q1 Included E-UTRA (LTE) and the Evolved Packet Core (SAE) architecture and further enhancements of HSPA (MIMO with 64QAM modulation and dual carrier with 64QAM modulation) 1.2 Mobile WiMAX The IEEE 802.16 Working Group on access equipment that conforms to broadband wireless access standards, IEEE 802.16 and the ETSI HiperMAN standard. established by the IEEE Standards Board in The WiMAX Forum defines and conducts 1999, prepared the formal specifications for conformance and interoperability testing to broadband wireless metropolitan area ensure that different vendor systems work networks (WirelessMAN, the 802.16 family of seamlessly with each other. WiMAX standards is the basis of Mobile WiMAX). certification profiles specify characteristics IEEE 802.16-2004 (also called 802.16d) such as spectrum band, duplexing and provides support for non-line-of-sight (NLOS) channelization. Several profiles exist for Fixed and indoor end-user terminals for fixed and Mobile WiMAX. wireless broadband. In 2005, the standard was amended (IEEE 802.16e-2005 or There are currently two waves of 802.16e) to add support for data mobility. certification planned for Mobile IEEE 802.16e or Mobile WiMAX improves WiMAX equipment: on the modulation schemes used in the ✒ Wave 1: Mobile WiMAX system profile with original (Fixed) WiMAX standard by single-input single-output (SISO) terminals introducing scalable orthogonal frequency- for the 2.3GHz and 3.5GHz bands division multiple access (SOFDMA ). ✒ Wave 2: Mobile WiMAX system profile with The system profile in IEEE 802.16e-2005 is multiple-input multiple-output (MIMO) not backward compatible with the Fixed terminals and beam-forming support for WiMAX system profile. the 2.6GHz band (sometimes referred to The charter of the WiMAX Forum, which as the 2.5GHz band). has more than 400 members, is to promote and certify the compatibility and Because IEEE 802.16 standardization only interoperability of broadband wireless covers basic connectivity up to the media Technical overview and performance of HSPA and Mobile WiMAX Introduction 5
  • 6. access (MAC) level, the WiMAX Forum also full IMS interworking, carrier-grade VoIP, addresses network architecture issues for broadcast applications, such as mobile TV, Mobile WiMAX networks. The first network and over-the-air provisioning. While Mobile architecture specification (Release 1.0) WiMAX offers the promise of high-speed focused on delivering a wireless internet wireless broadband services, it is still very service with mobility. much in its infancy and real-life performance Release 1.5 introduced support for has yet to be proved. telecom-grade mobile services, supporting Table 2: Evolution of WirelessMAN (802.16 family of standards) Version Released Info IEEE 802.16d 2004 Q2 Replaced all previous 802.16 specifications. Support for IEEE 802.16-2004 non-line-of-sight operation IEEE 802.16e 2005 Q4 Enhanced 802.16-2004 with support for data mobility IEEE 802.16e-2005 WiMAX Forum Network 2007 Q1 Networking specifications for fixed, nomadic, portable Architecture Specification and mobile WiMAX systems. Release 1.0 covers Release 1.0 internet applications and data mobility WiMAX Forum Network 2008 Q3 Enhancements to the Release 1.0 specification for Architecture Specification carrier-grade VoIP, location-based services, MBMS, full Release 1.5 IMS interworking and over-the-air client provisioning 6 Technical overview and performance of HSPA and Mobile WiMAX Introduction
  • 7. 2 Technical comparison HSPA and Mobile WiMAX technologies have mechanism, and operating frequency bands. been designed for high-speed packet-data This chapter provides a high-level description services. They feature similar technology of the similarities and differences between enablers, including dynamic scheduling, link HSPA and Mobile WiMAX. Technical details adaptation, HARQ with soft combining, of HSPA can be found in the 3GPP multiple-level QoS, and advanced antenna specifications. Likewise, details of Mobile systems. Notwithstanding, their performance WiMAX can be found in the IEEE 802.16e- differs due to differences in the physical layer 2005 standard and the WiMAX Forum Mobile signal format, duplex scheme, handover System Profile. 2.1 Similarities 2.1.1 Dynamic scheduling Traditional circuit-switched telephone channels, radio links often experience systems set up connections as dedicated fluctuations in signal strength. It is thus links for an entire session. This approach more effective to schedule the base station wastes communication resources for packet and terminal to communicate only when data because the dedicated link is tied up radio conditions are good. HSPA and even during idle periods. For high-speed Mobile WiMAX systems use channel- packet-data systems with bursty traffic, it dependent scheduling techniques makes better sense to allocate radio (Figure 1) to make efficient and effective resources only during active periods. use of packet-data resources. Given the volatile nature of wireless Scheduling: determines which end user to transmit to, at a given moment Channel-dependent Scheduling: transmit at fading peaks Figure 1: Channel-dependent scheduling Technical overview and performance of HSPA and Mobile WiMAX Technical comparison 7
  • 8. 2.1.2 Link adaptation When a mobile device is scheduled for HSPA and Mobile WiMAX support dynamic transmission, the quality of its radio link will selection between QPSK, 16QAM and vary in time. The modulation scheme and 64QAM modulation schemes, as well as of channel-coding rate used for a scheduled link the channel-coding rate, where the lowest can be adapted to minimize errors under a coding rate without repetition is 1/2 for variety of radio conditions. Link adaptation Mobile WiMAX and 1/3 (additional coding (Figure 2) enables full utilization of channel gain) for HSPA. Overall, HSPA has finer capacity for each communication link in the granularity of modulation and coding formats wireless environment and so maximizes the than Mobile WiMAX. throughput of scheduling-based systems. Adjust transmission parameters and match instantaneous channel conditions Figure 2: Link adaptation 8 Technical overview and performance of HSPA and Mobile WiMAX Technical comparison
  • 9. 2.1.3 H-ARQ with soft combining Because of delays in channel quality feedback, On the uplink, H-ARQ with soft combining link adaptation may suffer from errors also reduces transmission power and incurred between time instances of reporting improves system capacity, thanks to lower and scheduling. Hybrid acknowledgement interference and more stable power control. request (H-ARQ) with soft combining on the In HSPA, incremental redundancy is used for downlink and uplink quickly corrects these extra coding gain of the lower coding rate error packets without having to rely on that goes along with the retransmission. In higher-layer automatic repeat request (ARQ). Mobile WiMAX, only Chase combining is H-ARQ with soft combining is an effective available for energy gain; the coding rate is remedy to link adaptation errors and reduces not adjusted after retransmission. retransmission delays that are vital for higher- layer throughput. Figure 3: Hybrid acknowledgement request (H-ARQ) with soft combining 2.1.4 Multilevel QoS HSPA and Mobile WiMAX support multiple mechanisms defined for different QoS levels QoS levels. In HSPA, QoS levels are divided in the uplink: unsolicited grant service (UGS), into four categories: conversational, extended real-time polling service (ertPS), streaming, interactive, and background. In real-time polling service (rtPS), non-real-time Mobile WiMAX, there are five scheduling polling service (nrtPS), and best-effort. Technical overview and performance of HSPA and Mobile WiMAX Technical comparison 9
  • 10. 2.1.5 Advanced antenna technologies Advanced multiple antenna technologies instantaneous downlink channel conditions. improve the performance and capability of Therefore, in addition to diversity, WCDMA modern mobile communication systems closed-loop transmit diversity allows for (Figure 4). In general, they rely on the use beam-forming gains. of multiple transmit and receiver antennas WCDMA open-loop and closed-loop to achieve: transmit diversity are also available for HSPA. ✒ diversity against fading on the In addition, 2x2 spatial multiplexing (in HSPA radio channel Release 7) effectively doubles downlink peak ✒ beam-forming, to improve the radio link data rates. signal-to-noise/interference ratio The Mobile WiMAX system profile ✒ spatial multiplexing, often referred to as specifies two types of multi-antenna multiple-input multiple-output (MIMO) transmission schemes: antenna processing, to increase the ✒ transmit diversity using the Alamouti peak data rates and make more efficient space-time code (STC), which is similar to use of high radio-link signal-to-noise/ WCDMA/HSPA open-loop transmit interference ratios. diversity; and ✒ spatial multiplexing (MIMO). WCDMA supports two multi-antenna transmission schemes: open-loop transmit Mobile WiMAX also supports beam-forming, diversity, and closed-loop transmit diversity. which is enabled by uplink sounding. By WCDMA open-loop transmit diversity uses taking advantage of TDD channel reciprocity, modified Alamouti coding and can be applied the spatial characteristics measured at the to dedicated as well as common channels. base station can be used to form downlink Open-loop transmit diversity guards against beams. In practice, however, performance is radio-channel fading. WCDMA closed-loop limited by the asymmetry of interference and transmit diversity allows for adjustment of different antenna settings at the terminal and transmission phase and amplitude, based on base station. Figure 4: Overview of different antenna transmission schemes 10 Technical overview and performance of HSPA and Mobile WiMAX Technical comparison
  • 11. 2.2 Differences 2.2.1 Physical signal format The main differences between Mobile WiMAX uplink multiple accesses, Mobile WiMAX and HSPA in the physical layer are in the base stations must fine tune the frequency signal format. Mobile WiMAX is based on errors of each terminal within tolerable orthogonal frequency domain multiplexing ranges, and minimize the total interference (OFDM), whereas HSPA is a direct-sequence level by means of power control. spread-spectrum system. One of the most In addition, OFDM signals have a relatively important features of OFDM is its robustness large peak-to-average power ratio (PAPR), to multipath propagation. The key enabler of which means that for a given average power, this feature is the use of narrowband tones in the power amplifier must be able to handle combination with a cyclic prefix. The cyclic very high power peaks without distorting the prefix serves two purposes: it provides a transmitted signal. guard time against inter-symbol interference, HSPA uses CDM code aggregation and it ensures that the multipath channel only (orthogonal Walsh code) to offer a high-speed imposes a scalar distortion on each tone, downlink channel, and direct-sequence code- making equalization simple and effective. division multiple access (CDMA) for the When properly synchronized and protected uplink. While this method is less sensitive to by cyclic prefix, tones of an OFDM signal Doppler spread, the loss of orthogonality in remain mutually orthogonal even after going time-dispersive channels creates intra-cell through multipath channels. The interference that limits the use of high-order disadvantage of using cyclic prefix is modulation. Generalized RAKE receivers increased overhead, which effectively can alleviate interference through advanced reduces bandwidth efficiency. signal processing on the receiver side The ability of an OFDM signal to maintain at the moderate cost of additional orthogonality under multipath conditions receiver complexity. gives an intra-cell interference-free system When compared with OFDM signals, the that is well suited to high-speed data HSPA uplink signals have lower PAPR— transmission. Notwithstanding, inter-tone which implies a less complex power amplifier. interference arises (degrading performance) Alternatively, for a given complexity, a when there are large Doppler spreads in higher average power can be used, giving OFDM. When OFDM signals are used for greater coverage. 2.2.2 Duplex scheme One other difference between HSPA and channels, one for the uplink and one for Mobile WiMAX is the duplex scheme. HSPA the downlink). is an FDD technology, with uplink and The Mobile WiMAX system profile, as downlink transmission taking place in currently defined in the WiMAX Forum, is a separate frequency channels (usually denoted TDD technology with just one frequency as 2x5MHz to indicate two separate 5MHz channel (10MHz for example) that is shared in Technical overview and performance of HSPA and Mobile WiMAX Technical comparison 11
  • 12. Figure 5: Overview of FDD and TDD the time domain between the uplink and The interference scenarios are different downlink. The ratio between the uplink and between FDD and TDD systems (Figure 6). downlink defines how the frequency channel FDD systems use a frequency duplex gap is shared. A 2:1 ratio means the channel is between the uplink and the downlink to used two-thirds of the time for the downlink prevent interference between transmissions. and one-third of the time for the uplink TDD systems use a guard time between the (Figure 5). uplink and downlink. The IEEE 802.16 specification allows for When building a TDD network, one must FDD operation, but to date, the Mobile deal with a variety of interference scenarios: WiMAX system profile solely stipulates TDD. ✒ Interference within a network – TDD has the flexibility of changing the interference between base stations and downlink-to-uplink ratio to accommodate a between terminals. All the base stations variety of traffic asymmetries, although in must be fully time-synchronized with each practice the ratio needs to be fixed system- other (for example, using a GPS receiver at wide (unless guard bands are used to limit each base station). interference effects). In addition, TDD ✒ Between a network and an adjacent systems with a large downlink-to-uplink ratio, TDD network – two or more TDD have a link budget penalty as the uplink networks using the same frequency band average power is reduced for a given in the same geographical area. To avoid peak power. interference, synchronization must be Figure 6: Overview of interference scenarios for FDD and TDD systems 12 Technical overview and performance of HSPA and Mobile WiMAX Technical comparison
  • 13. coordinated between neighboring can only be resolved using suitable networks, or guard bands must be used. guard bands. This scenario might occur at national or ✒ Duty cycle uplink/downlink settings in state borders, especially where only local the TDD network relative to adjacent licenses have been issued. networks—in addition to synchronization ✒ Between a network and a spectrum- in time, when setting the uplink/downlink adjacent TDD network—one TDD ratio in a TDD network, the ratio within the network uses adjacent frequencies, giving network and with neighboring networks rise to base station to base station must be coordinated, to avoid all the interference if the base stations from the interference cases mentioned above. different networks are in close proximity. Alternatively, guard bands can be used. The uplink to one base station can suffer interference from out of band leakage from Stringent requirements from existing another base station. This interference can satellite services in specific bands make it be reduced by synchronizing the difficult to deploy TDD technologies in these networks, or by using guard bands. frequencies. The tougher coexistence ✒ FDD and TDD spectrum borders—an environment for TDD puts heavy requirements FDD network uses frequencies adjacent to on the RF filters, which are just as complex as the TDD network, giving rise to base the duplex filter requirements for FDD. station to base station interference if the The 3GPP specification covers FDD and base stations from the different networks TDD, but there have not been any major are in close proximity. This interference deployments of TDD-based cellular systems. 2.2.3 Handover mechanism HSPA supports soft handover in the uplink, Hard handover is used for intra-frequency which yields macro-combining gain and handover and intersystem handover to GSM. improves the link budget (by 1.5dB on The Mobile WiMAX system profile includes average). It also helps increase network only hard handover. capacity by reducing intra-cell interference. 2.2.4 Operating frequency bands HSPA currently supports frequency bands Several frequency bands are under ranging from 800MHz to 2,600MHz, including discussion for Mobile WiMAX, but current most current 2G operating bands in Europe, certification profiles only cover the 2.3GHz, Africa, the Americas and Asia-Pacific. The 2.6GHz and 3.3–3.8GHz frequency bands. At most common bands for HSPA are 2.1GHz, present, there are only a few deployments of deployed worldwide, and the 850MHz band Mobile WiMAX, mainly in the 2.3GHz and deployed in the Americas, Australia, New 2.6GHz bands. Zealand, and parts of Asia. Approximately 90 percent of all spectrum allocations worldwide are FDD. Technical overview and performance of HSPA and Mobile WiMAX Technical comparison 13
  • 14. 2.3 Summary technical comparison Table 3 summarizes the technical similarities and differences between HSPA and Mobile WiMAX. Table 3.Technical comparison of HSPA and Mobile WiMAX HSPA Mobile WiMAX Physical signal format DL code aggregation, OFDMA for both DL and UL UL DS-CDMA Hybrid ARQ with soft Adaptive IR + Chase Chase combining combining combining Multi-level QoS √ √ Link adaptation QPSK, 16QAM, 64QAM QPSK, 16QAM, 64QAM Lowest code rate: 1/3 Lowest code rate: 1/2 Duplex scheme FDD TDD Frequency bands 850MHz to 2,600MHz 2.3GHz, 2.6GHz and 3.4–3.8GHz Handover Hard handover, Hard handover soft handover Frequency reuse one √ √ Advance antenna • Closed- and open-loop • Open-loop transmit diversity technologies transmit diversity • Spatial multiplexing • Spatial multiplexing • Beam forming • Beam forming 14 Technical overview and performance of HSPA and Mobile WiMAX Technical comparison
  • 15. 3 Performance characteristics Vital characteristics of system performance which might give a misleading picture – the are data rates, delay, spectrum efficiency and discourse covers a set of HSPA and Mobile coverage. For end users, these WiMAX releases, to enable a fair comparison. characteristics determine which services can Because many features are common to both be offered. For operators, they define number system families – including antenna (MIMO) of users and base station coverage area, concepts, modulation and channel coding – which directly influences the cost of operating performance is similar in many respects. the system. There are some differences, however, such as This chapter presents the performance the duplex scheme, frequency bands, characteristics of HSPA and Mobile WiMAX in multiple-access technology and design of the terms of peak data rates, spectrum efficiency control channel, which give rise to and coverage. Rather than cover just one differences, for example, in uplink bit rates version (or release) of each system family – and coverage. 3.1 Peak data rates The peak data rate indicates the bit rate a data rates, measured above the MAC layer, user in good radio conditions can reach when for a set of system concepts. Early releases the channel is not shared with other users. of HSPA (Release 6) and Mobile WiMAX Figure 7 shows the downlink and uplink peak Wave 1 achieve comparable peak rates. Figure 7: Peak data rates for a set of HSPA releases and WiMAX waves. For WiMAX, the TDD symmetry is expressed in terms of number of downlink and uplink slots for data (that is, 28:15). The use of multistream MIMO is indicated by a factor in front of the modulation scheme. Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics 15
  • 16. Mobile WiMAX uses higher-level modulation same modulation formats (64QAM and (64QAM in the downlink and 16QAM in uplink) 16QAM) and comparable MIMO schemes than HSPA release 6, which uses 16QAM in (two streams in the downlink) are used, but the downlink and QPSK in the uplink. HSPA HSPA has less overhead. Release 8 also Release 7 introduces 64QAM and two-stream supports downlink transmission using 2 MIMO in the downlink (but not for carriers with 64QAM, which gives the same simultaneous use) and offers comparable peak rate as MIMO + 64QAM. performance to Mobile WiMAX Wave 2. The Mobile WiMAX may use TDD asymmetries peak data rate of HSPA Release 8 betters that to increase downlink peak data rates at the of Mobile WiMAX Wave 2. In this case, the expense of reduced uplink peak data rates. 3.2 Spectrum efficiency Spectrum efficiency measures the maximum traffic load per user, spectral efficiency can total amount of data that can be carried by a be used to determine the number of users a cell per unit of time, normalized with the cell can support (Figure 8). occupied system bandwidth. For any given Figure 8. Spectrum efficiency comparisons (Note that absolute spectrum efficiency values vary with models and assumptions—the above values should only be used for relative comparisons). 16 Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics
  • 17. The spectrum efficiency figures have been RAKE receivers (indicated by the dotted line evaluated using models, assumptions and in Figure 8). However, with more advanced methodology aligned with 3GPP standards receivers, such as G-RAKE with receive (in this case, a system with 19 three-sector diversity, HSPA has substantially better sites, placed on a regular grid with 500m spectrum efficiency – a comparison of HSPA inter-site distance).[1] “Full-buffer” type users Release 6 with advanced receivers shows are uniformly distributed. The selected that HSPA has greater spectrum efficiency. propagation models (which model spatial HSPA Release 7 is modeled with two-stream correlation between antennas to enable MIMO in the downlink and 16QAM in the accurate MIMO evaluations) simulate an uplink. Mobile WiMAX Wave 2 performance is urban environment. comparable to HSPA Release 7. System models, such as antenna solutions HSPA Release 8 shows better spectrum and output powers, have been aligned with efficiency than Mobile WiMAX Wave 2. the capabilities of the studied systems. These results are similar to those presented Similar assumptions have been made for all by 3G Americas.[2] The figures for Mobile systems, with the aim of achieving fair WiMAX are somewhat lower than those comparisons. Note: the figures should only presented by WiMAX Forum, probably be used for comparative purposes and not as because of differences in modeling.[4] The absolute values. WiMAX Forum does not present results for The spectrum efficiency achieved by HSPA HSPA Release 7 or 8. Its results for HSPA Release 6 is dependent on receiver type. Release 6 are similar to those presented here Mobile WiMAX Wave 1 has better spectrum and assume simple receivers. efficiency than HSPA Release 6 with basic 3.3 Coverage Coverage is a crucial metric of performance, specific case. Relative comparisons of link because it determines the number of sites budgets for different system concepts are needed to deploy a complete network, and informative and easy to make. HSPA and the data rate available at a given distance in a Mobile WiMAX have distinctive given deployment. A common way of characteristics that affect the link budget, measuring coverage is to use link budgets, including output power, duplex method which provide an estimate of the maximum and frequency band—especially on the path loss the system can sustain between the uplink, which is typically the limiting link. base station and terminal. Figure 9 summarizes the impact of Accurate absolute link budgets depend on these characteristics. several factors and are best simulated for a Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics 17
  • 18. Figure 9: HSPA typically has 6-10dB greater coverage than Mobile WiMAX Using typical terminal power classes, the operating at about 2.0GHz, the path loss maximum output power of Mobile WiMAX increases by a factor of (2.6/2.0)2 = 1.7, terminals (23dBm) is 1dB lower for than for or 2.3dB. At 3.5GHz the corresponding HSPA (24dBm). This constitutes a difference figure is 4.9dB. of 1dB in the link budget. One reason for this Apart from these differences, soft handover disparity is the difference in uplink modulation in HSPA improves coverage, and lower and multiple access methods. overhead improves sensitivity. With TDD, if the link is used only half the In summary, although Mobile WiMAX and time for a given average data rate, then the HSPA are based on similar techniques, the transmission data rate must be twice as high. link budget of Mobile WiMAX can be as much If the link is used one-quarter of the time, as 6dB lower than that of HSPA. In a then the transmission data rate must be four coverage-limited network, this translates into times as high. Radio links to terminals at the the need for 2.2 times as many sites. This cell border are typically power-limited. This figure is derived on the basis of d3.5 means that the achievable bit rate is propagation (which is typical in urban and proportional to the transmitted power but suburban areas). In this case, a 6dB increase insensitive to channel bandwidth. To in path loss (a factor of four) corresponds to a compensate for this loss, the terminal must distance coverage loss of a factor of 41/3.5 = have better path loss—by a factor 2 (3dB) or 1.5, or an area coverage loss of a factor of 4 (6dB) for activity factors of 50 percent and 1.52 = 2.2. In rural areas, which have lower 25 percent, respectively. path loss exponents, the differences are Deploying Mobile WiMAX in higher even larger. frequency bands than are typically used for For coverage-driven deployment, Mobile HSPA will result in additional loss in the link WiMAX at 2.6GHz would need approximately budget. Path loss is proportional to the 2.3 to 3.4 times as many sites than HSPA at square of the frequency. Given Mobile WiMAX 2.1GHz. Even compared with HSPA at 2.6 operating in the 2.6GHz band, HSPA GHz, Mobile WiMAX increases the site count operating in the 2.1GHz band, and the uplink by approximately 1.7 to 2.5 times. 18 Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics
  • 19. 3.4 Real-life experience HSDPA became commercially available in Better still, the first terminals to support 15 2005 and has since been rolled out for codes and 64QAM modulation are now commercial operation in networks around becoming available. Initial tests show that the world. these terminals can support average bit rates Initially, user terminals were limited to five of more than 10Mbps. codes and 16QAM modulation, giving a HSPA is a mature technology which offers theoretical maximum data rate of 3.6Mbps. mobile broadband services that rival the Feedback from live networks shows that the performance of fixed broadband networks actual rates are close to the theoretical (such as ADSL and cable). Load calculations simulations (Figure 10). in an HSPA network show that with a 10GB Many user terminals now support 10 codes monthly “bit bucket,” operators can deliver and have a theoretical maximum data rate of a commercially viable flat-rate mobile 7.2Mbps (Figure 11). In commercial networks broadband service to every subscriber these terminals give impressive results with in the network. user data rates of up to 6Mbps. Figure 10: HSPA performance measured in a live commercial network Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics 19
  • 20. Figure 11: HSPA performance measured on a commercial system using a terminal that supports up to 7.2Mbps 20 Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics
  • 21. 4 Network architecture The 3GPP is a collaboration between several with HSPA, 3GPP Release 7 enhanced the telecommunications standards bodies. It reference architecture (Figure 12) with a 3G handles GSM and WCDMA standardization direct tunnel that optimizes the delivery of for the complete mobile system, including mobile and wireless broadband services. terminal aspects, radio access networks, Compared with 3GPP Release 6 and earlier core networks, and parts of the architectures, the direct tunnel architecture service network. provides a direct data path from the RNC to The air interface, as well as the network, is the GGSN, increasing topological flexibility progressively being improved with every and improving latency. advance in the 3GPP specification. In step Figure 12: Overview of the 3GPP reference architecture Technical overview and performance of HSPA and Mobile WiMAX Network architecture 21
  • 22. 4.1 WiMAX Forum and IEEE Figure 13: Mobile WiMAX network architecture The IEEE 802.16 standard covers the air • Split management of radio resources, interface (IEEE 802.16e) and basic with a radio resource agent in the base connectivity up to the media access (MAC) station and a radio resource controller level. The WiMAX Forum defined the network in the ASN-GW. architecture specifications for WiMAX • Open interfaces for Profile A: R1, R6, networks (Figure 13). The first specification R4, and R3. (Release 1.0) focuses on delivering internet ✒ Profile B: services with mobility. At present, the network • ASN solution where the base station architecture defines three RAN profiles and ASN-GW functions are (Profile A, Profile B, Profile C), each with a implemented on a single platform. different functional allocation: • Open interfaces Profile B: R4 and R3. ✒ Profile A: ✒ Profile C: • ASN model with base station and ASN • Similar to Profile A except that radio gateway (ASN-GW) implemented on resource management is not split but is separate platforms, interacting through located entirely in the base station. the R6 interface. 22 Technical overview and performance of HSPA and Mobile WiMAX Network architecture
  • 23. 4.2 Architecture comparison Figure 14 compares the Mobile WiMAX However, using IP tunneling protocols to architecture with the 3GPP Release 7 meet the need for wireless mobility requires a architecture for mobile broadband services. lot of functionality in areas such as bearer The target requirements are broadly similar in management, QoS, charging, radio access terms of functional allocations and architecture. type information, and more. From the outset, However, the selection of protocols in each GTP was tailored to support this functionality. standards organization has been influenced by This differs from the approach of the WiMAX the chosen technology. 3GPP builds on GTP Forum, which has instead extended the and DIAMETER, which provide optimized inter- baseline IETF protocols to include wireless- working with legacy GSM terminals and specific functionality and to deploy multiple common anchoring in the GGSN for dual-mode protocols in parallel over the same interface. GSM/WCDMA/HSPA terminals. In addition, At a high level, RADIUS and DIAMETER GTP provides an efficient way of handling QoS look similar. Both were developed by IETF, and of creating binding to radio bearers. The and DIAMETER is an evolved version of WiMAX Forum, by contrast, has gone with RADIUS. DIAMETER is widely used within Mobile IP and RADIUS; it also supports PMIP IMS specifications and provides functionality and CMIP for both IPV4 and IPV6. beyond RADIUS, mainly in the area of carrier- A comparison of Mobile IP and GTP reveals grade performance. This translates into several similarities in terms of functionality. For functionality, such as standardized instance, the protocols solve the same types of application packages (instead of vendor- problems in areas such as session specific attributes), reliable transport management, user plane tunnel setup for IPv4 layer, bidirectional communication, and and IPv6 payload, and multiple packet sessions heartbeat mechanisms. Figure 14: HSPA and Mobile WiMAX network architectures Technical overview and performance of HSPA and Mobile WiMAX Network architecture 23
  • 24. 4.3 System Architecture Evolution The system architecture evolution (SAE), The mobility management entity (MME), an specified together with LTE, is the next step evolution of the SGSN server, has been in the 3GPP architecture evolution. It will specified for 3G Direct Tunnel functionality in deliver a flattened network architecture 3GPP Release 7. In all likelihood many with simplified QoS, for the delivery of IP implementations will co-locate the MME with services (Figure 15). the SGSN. SAE is an evolution of 3GPP Release 7, The SAE-GW node will include evolved with support for 3GPP LTE and non-3GPP GGSN functionalities including IP networking access technologies, as well as current 2G interfaces and end-user IP point of presence, and 3G access technologies. shallow and deep packet inspection, as well The architecture splits packet core control as real-time charging, policy control, and and user plane functionality into separate mobility to non-3GPP accesses using mobile nodes. Moreover, it further optimizes the IP. What is more, operators who evolve their HSPA architecture for mobile broadband networks to LTE/SAE from GSM/WCDMA/ services with two nodes (eNodeB and SAE HSPA will enjoy full backward compatibility gateway, SAE-GW) in the user plane for the with legacy networks. main use cases. Figure 15: Overview of the SAE architecture 4.4 Mobile WiMAX Details of the network architecture evolution functionality, such as policy management and for Mobile WiMAX beyond Release 1.0, IMS support, prepaid support, emergency approved in March 2007, is described in services, and roaming. Release 1.5, which includes enhanced 24 Technical overview and performance of HSPA and Mobile WiMAX Network architecture
  • 25. 5 Conclusion Given that HSPA and Mobile WiMAX employ factors help ensure nationwide coverage many of the same techniques, their for voice (GSM/WCDMA) and data performance is comparable in many areas. (HSPA/EDGE). However, key differences in areas such as Thanks to its heritage, HSPA gives duplex mode (FDD versus TDD), frequency operators a single network for multiple bands, multiple access technology, and services with a sound business case built on control channel design give rise to differences revenues from voice, SMS, MMS, roaming, in uplink bit rates and coverage. and mobile broadband. While the peak data rates, spectral HSPA offers an ecosystem of unrivalled efficiency and network architecture of HSPA breadth and depth as well as unmatched Evolution and Mobile WiMAX are similar, economies of scale that benefit all players in HSPA offers better coverage. In short, Mobile the ecosystem, which currently serves more WiMAX does not offer any technology than 2 billion subscribers. advantage over HSPA. Operator choices of technology today will What is more, HSPA is a proven mobile influence operations for many years to come. broadband technology deployed in more than The good news in this context is that 3GSM 250 commercial networks. It is built on the technologies are future-proof in terms of initial firm foundations of the 3GPP family, offering investment, economies of scale, and the users the broadband speeds they want and ability to extend and continuously enhance the carrier-grade voice services they expect. the solution. HSPA can be built out using existing GSM Compared with other alternatives, HSPA is radio network sites and is a software upgrade the clear and undisputed choice for mobile of installed WCDMA networks. When used broadband services. together with dual-mode terminals, these Technical overview and performance of HSPA and Mobile WiMAX Conclusion 25
  • 26. 6 Glossary AAA authentication, authorization and accounting ASN access service network BS base station CDMA code division multiple access CSCF Call Session Control Function DSL digital subscriber line EDGE Enhanced Data rates for Global Evolution FA/HA Foreign Agent/Home Agent FDD frequency division duplexing GGSN gateway GPRS support node GPRS General Packet Radio Service GSM Global System for Mobile communications G-RAKE receiver generalized RAKE receiver HSPA High Speed Packet Access – an extension of WCDMA to provide high bandwidth and enhanced support for interactive, background, and streaming services HSS Home Subscriber Server IEEE Institute of Electrical and Electronics Engineers IMS IP Multimedia Subsystem IPR intellectual property rights ITU International Telecommunication Union MAC Media Access Control MIMO multiple input, multiple output MME mobility management entity OFDM orthogonal frequency division multiplexing – a digital encoding and modulation technology used by 802.16-based systems (including WiMAX) as the air interface PCRF Policy Charging Rule Function PDG packet data gateway RAKE receiver a radio receiver designed to counter the effects of multipath fading RX receiving antennas SAE-GW system architecture evolution gateway SGSN serving GPRS support node TDD time division duplexing TTG tunnel termination gateway TX transmitting antennas WAG wireless access gateway WCDMA Wideband Code Division Multiple Access – a wideband spread-spectrum 3G mobile telecommunication air interface WiMAX Worldwide Interoperability for Microwave Access – a standards-based technology that enables the delivery of last mile wireless broadband access as an alternative to cable and DSL VoIP Voice over IP technology enables users to transmit voice calls via the internet using packet-linked routes; also known as IP telephony. 3G Third-generation radio technology for mobile networks, telephones and other devices. Narrowband digital radio is the second generation of technology 3GPP Third Generation Partnership Project, a collaboration agreement that brings together a number of telecommunications standards bodies 3G LTE/SAE 3G Long Term Evolution/System Architecture Evolution 26 Technical overview and performance of HSPA and Mobile WiMAX Glossary
  • 27. 7 References [1] 3GPP. October 2006. TR 25.814, Physical layer aspect for evolved Universal Terrestrial Radio Access (UTRA). Available at: http://www.3gpp.org/ftp/Specs/html-info/25814.htm [Accessed 8 December 2008]. [2] 3G Americas. September 2006. Mobile Broadband: EDGE, HSPA and LTE. Available at: http://www.3gamericas.org/documents/2006_Rysavy_Data_Paper_ FINAL_09.15.06.pdf [Accessed 8 December 2008]. [3] 3rd Generation Partnership Project (3GPP). http://www.3gpp.org/ [Accessed 8 December 2008]. [4] WiMAX Forum, http://www.wimaxforum.org/ [Accessed 8 December 2008]. [5] IEEE-SA. June 2004. IEEE 802.16-2004 Air Interface for Fixed Broadband Wireless Access Systems. Part 3: Radio Conformance Tests (RCT)for 10–66 GHz WirelessMAN-SC™ Air Interface. Available at: http://standards.ieee.org/getieee802/download/802.16_Conformance03-2004.pdf Accessed 8 December 2008]. [6] IEEE-SA. February 2006. IEEE 802.16e-2005 Air Interface for Fixed and Mobile Broadband Wireless Access Systems. Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems. Available at: http://standards.ieee.org/getieee802/download/802.16e-2005.pdf [Accessed 8 December 2008]. Technical overview and performance of HSPA and Mobile WiMAX References 27