advances wireless networks

2. Ultra-Wide Band
• Signal Emission Approach:
– UWB radios use short pulses in the picosecond (ps) to nanosecond (ns) range.
– Bluetooth and 802.15.4 emit signals over long periods using a small part of the spectrum.
• Bandwidth Utilization:
– UWB utilizes a large bandwidth, often spanning many gigahertz.
– Bluetooth and 802.15.4 use a small part of the spectrum for signal transmission.
• Data Rate and Power Efficiency:
– According to Shannon's Law, UWB achieves high data rates (hundreds of Mbps or several Gbps) more
efficiently by increasing bandwidth rather than power.
– UWB radios offer high data rates with relatively low power consumption.
• Signal Characteristics:
– UWB signals use short pulses over a wide spectrum, ensuring signals are below the FCC-defined noise
threshold (-41.3 dBm/MHz).
– UWB signals are less susceptible to noise or jamming due to their unique emission characteristics.
• Technology Complexity:
– UWB is a simpler technology compared to Bluetooth and ZigBee.
– Currently, there are no mandatory or optional middleware layers built on top of UWB's basic PHY (Physical
Layer) and MAC (Media Access Control) layers.
• Standards Competition:
– There are currently two major competing UWB standards in the industry.
– IEEE is making efforts to create a unified UWB standard to streamline compatibility and interoperability.
• Unified Standard Development:
– IEEE is actively involved in developing a unified UWB standard to bring cohesion to the diverse UWB
landscape.
• Future Applications:
– UWB technology holds potential for various future applications beyond current uses.

3. Direct Sequence-UWB (UWB Forum)

4. • DS-UWB Radios Characteristics:
– DS-UWB radios utilize a single pulse, as depicted in Figure 4.
– Signals are transmitted in one of two spectra: 3.1 GHz - 4.85 GHz or 6.2 GHz - 9.7 GHz.
• Spectrum Parameters:
– DS-UWB spectrum supports a range of parameters impacting the usable data rate.
– Pulse modulation can be either 4-BOK (2 bits/signal) or BPSK (1 bit/signal) based on signal quality and data
rate requirements.
• Forward Error Correction (FEC):
– DS-UWB allows optional FEC with rates of 1/2, 3/4, or 1 to enhance error resilience in transmission.
• Code Sequences:
– DS-UWB radios employ code sequences using 1 to 24 pulses to transmit a bit, depending on signal quality.
• Data Rate Variability:
– Depending on selected parameters, DS-UWB radios can achieve data rates ranging from 55 Mbps to 1.32
Gbps in the 3.1 GHz band and 55 Mbps to 2 Gbps in the 6.2 GHz band.
• Standardization by UWB Forum:
– DS-UWB is standardized by the UWB Forum.
– The standard includes a MAC layer for DS-UWB-based devices.
• MAC Layer Features:
– The UWB Forum's standard MAC layer for DS-UWB devices utilizes code division, offset operating
frequencies, and FDM.
– These features enable multiple piconets to appear as white noise to each other, reducing or eliminating the
need to resolve media contention among nearby Personal Area Networks (PANs).
• Limited Accessibility of Specifications:
– Unfortunately, detailed technical specifications of the DS-UWB MAC layer by the UWB Forum are not
publicly available.
– The UWB Forum FAQ mentions the use of code division, offset operating frequencies, and FDM to mitigate
contention among PANs.

5. Multi-Band OFDM (WiMedia)

6. • MB-OFDM Signaling Approach:
– MB-OFDM divides the spectrum into multiple sub-bands, contrasting with DS-UWB's use of a single pulse over a wide band.
• Frequency Hopping Scheme:
– MB-OFDM signals hop across sub-bands in a predictable manner, with frequency changes every 312.5 ns and a 9.5 ns guard
between hops.
– The spectrum used by MB-OFDM spans from 3.1 GHz to 10.6 GHz, divided into 14 equally-sized sub-bands of 528 MHz each.
• Data Rate and Tunable Parameters:
– Data rates in MB-OFDM vary based on encoding choices.
– MB-OFDM has fewer tunable parameters compared to DS-UWB.
– QPSK modulation (2 bits/signal) is used, and forward error correction rates of 1/3, 1/2, 5/8, or 3/4 are supported.
• Implementation Options:
– MB-OFDM radios can transmit coded transmissions over three sub-bands simultaneously or use a single band, providing
flexibility based on application requirements.
• Data Rate Range:
– Depending on selected parameters, MB-OFDM offers data rates ranging from 53.3 Mbps to 480 Mbps.
• WiMedia Alliance Standard:
– The MB-OFDM standard is defined by the WiMedia Alliance.
– While not IEEE-certified, it has been submitted to Ecma International and is accessible to the public.
• MAC Layer Features:
– WiMedia Alliance defines a MAC layer for use with MB-OFDM radios.
– The MAC layer supports unicast and broadcast packet transmission.
– Unicast packets are directed based on a 16-bit device address, with reserved addresses for broadcast groups.
• Addressing Scheme:
– Unlike Ethernet MAC addresses, WiMedia device addresses are not guaranteed to be globally unique.
– The WiMedia standard defines a scheme for resolving address conflicts.
• Reservation Mechanism:
– WiMedia devices can transmit special packets to reserve transmission slots or contend for non-reserved slots.
– Reservations in WiMedia are decentralized, contrasting with ZigBee's centralized coordinator node approach.

7. UWB Security
• Inherent Security Characteristics of UWB:
– UWB radios exhibit inherent security features due to low output power and short pulses, making their transmissions appear as white noise from a distance.
– Close proximity to the transmitter could potentially allow determined attackers to sniff UWB signals, necessitating security measures.
• Security at the MAC Layer:
– Security measures are mandated at the MAC layer for UWB radios to enhance confidentiality and prevent unauthorized access.
• UWB Forum's DS-UWB Security (Not Discussed):
– The UWB Forum's DS-UWB standard specifications are not publicly available.
– Therefore, a detailed discussion of security features employed by DS-UWB is not possible in this context.
• WiMedia's MAC-Level Security Features:
– WiMedia defines three levels of link-layer security to address potential vulnerabilities.
• Security Level 0:
– Devices in Security Level 0 send data fully unencrypted.
• Security Level 1:
– Devices supporting Security Level 1 establish encrypted links with other Level 1 devices.
– They can also establish unencrypted links with devices lacking encryption support.
• Security Level 2:
– Devices at Security Level 2 mandate that all links must be encrypted.
– These devices cannot establish links with devices in Security Levels 0 and 1.
• Encryption Mechanism:
– WiMedia devices use AES-128 for link-level encryption.
• Master Keys and MKID:
– Each device is equipped with one or more pre-defined 128-bit master keys.
– Master keys have corresponding master key IDs (MKID) to avoid plaintext transmission.
– Devices exchange MKIDs during connection to establish a common master key, then negotiate a unique per-link key.
• AES-128 Counter Mode:
– AES-128 operates in counter mode, XORing plaintext with an incremented counter for each message.
– This converts fixed master and link keys into temporal keys.
• Challenge/Response Handshaking:
– Devices use a challenge/response handshaking protocol during link establishment.
– Random nonces are exchanged to prevent replay attacks.
• Group Transient Key (GTK):
– For securing broadcast transmissions, each group has a common group transient key (GTK).
– GTKs are exchanged using a gossiping scheme during link establishment between devices.
• Unclear GTK Creation:
– WiMedia specification does not explicitly detail how GTKs are created initially, but it is assumed to be generated by the first device to join the group.

8. Applications
• Cable-Replacement Technology:
– UWB is positioned as a cable-replacement technology similar to Bluetooth but designed for devices with higher data-rate
requirements.
• Belkin's UWB-Enabled Product:
– In January 2006, Belkin introduced the first UWB-enabled product, a wireless USB hub using the DS-UWB-based CableFree
protocol.
• Wireless USB Standard Development:
– The USB Implementers Forum is working on an official Wireless USB standard.
– It will operate on the WiMedia stack, providing speeds up to 480 Mbps within a 3-meter range, comparable to USB 2.0.
• Bluetooth Integration:
– WiMedia standard will serve as the foundation for a future version of the Bluetooth radio layer.
• Home Theater Applications:
– UWB's high data rate supports HDTV streams, making it a potential replacement for audio/video cables in home theaters.
• Current Status and Challenges:
– UWB technology is still in its early stages with only a few announced products, none of which have been shipped.
• Incompatible Standards Issue:
– UWB technology is divided into two incompatible standards, potentially hindering market acceptance.
– The development of Freescale's CableFree standard independently of the UWB Forum may further fragment the market.
• Signal Quality Challenges:
– Due to the low average power of UWB radios, signal quality degrades rapidly as transmitter and receiver move apart.
– Wireless USB's data rate, for example, drops significantly from 480 Mbps to 110 Mbps when devices are separated by 10 meters.
• 802.15.5 Task Group and Mesh Networks:
– The forthcoming 802.15.5 standard allows UWB devices to form mesh networks, potentially mitigating signal quality issues.
– Mesh networks enable multi-hop links, allowing devices located far apart to communicate through a series of shorter, higher-
quality links.
• Standard Development Challenges:
– The 802.15.5 Task Group, like the 802.15.3c Task Group, has not produced any standards as of the current writing.
– The 802.15.5 standard may require MAC layer changes for full functionality, and devices deployed before its finalization might
not benefit from its features.