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Energy efficient wireless technology


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Measures to improve energy efficiency and spectral efficiency in a wireless communication system.

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Energy efficient wireless technology

  1. 1.  Green technology is the development and application of products, equipment and systems used to conserve the natural environment and resources, which minimizes and reduces the negative impact of human activities. CRITERIA OF GREEN TECHNOLOGY: It minimizes the degradation of the environment. It has a zero or low green house gas (GHG) emission. It conserves the use of energy and natural resources. Eisha Madhwal 5/30/2012 2
  2. 2.  Energy Efficiency: EE is defined as the number of bits transmitted per Joule of energy. Unit: bit/J Spectral Efficiency: SE refers to the information rate that can be transmitted over a given BW in a specific communication system. Unit: bit/s/Hz Area Spectral Efficiency: ASE is defined as the max. throughput-summed over all users in the system, divided by the channel BW. Unit: bit/s/Hz per unit area Eisha Madhwal 5/30/2012 3
  3. 3.  Eisha Madhwal 5/30/2012 4
  4. 4.  According to their definitions, SE and EE can be expressed as ----(2) ----(3) Putting the value of EE from (2) in (3) we get the SE-EE relationship as ------(4) Eisha Madhwal 5/30/2012 5
  5. 5. Fig. 1: Sketch of the trade-off relations without and with practicalconcerns [2] Eisha Madhwal 5/30/2012 6
  6. 6.  Impact of cell sizes on EE: Reducing the cell size can increase the no. of delivered information bits per unit energy for given user density and total power in the service area. If a sleep mode is introduced, the EE can be further enhanced. Eisha Madhwal 5/30/2012 7
  7. 7. Some advanced communication techniques fullyexploited in wireless networks to provide SE are: Orthogonal Frequency Division Multiple Access (OFDMA) Multiple –Input, Multiple –Output (MIMO) techniques Relay Transmission Eisha Madhwal 5/30/2012 8
  8. 8.  OFDMA is a multi-user OFDM that allows multiple access on the same channel (a group of evenly spaced subcarriers). Input data gets divided into several parallel sub- streams of reduced data-rate and each sub-stream is modulated and transmitted on a separate Orthogonal Subcarrier. Eisha Madhwal 5/30/2012 9
  9. 9. Fig. 2: Difference between OFDM & OFDMA [3] Eisha Madhwal 5/30/2012 10
  10. 10.  System resource, such as subcarriers & transmit power, needs to be properly allocated to different users to achieve high performance. Two schemes used for dynamic resource allocation are:1. Rate Adaptation (RA): maximizes the throughput. Aims at SE.2. Margin Adaptation (MA): Minimizes total transmit power. Aims on transmit power efficiency. Eisha Madhwal 5/30/2012 11
  11. 11.  Energy-efficient OFDM systems was first addressed with consideration of circuit consumption for frequency-selective fading channels. This scheme maximizes the overall EE by adjusting both- the total transmit power and its distribution among subcarriers. 15% reduction in energy consumption is observed when frequency diversity is exploited. Eisha Madhwal 5/30/2012 12
  12. 12.  Energy-efficient power distribution not only boosts system EE but also refines the EE-SE trade-off. The existing research on energy-efficient OFDMA has mainly focused on uplink scenarios or mobile terminal sides. More effort should be put on the downlink or BS sides for the green design target. General EE-SE trade-off is not yet addressed yet. Eisha Madhwal 5/30/2012 13
  13. 13.  MIMO (Multiple Input, Multiple Output) is an antenna technology for wireless communications in which multiple antennas are used at both the source (Tx) and the destination (Rx). The antennas at each end of the communication circuit are combined to minimize errors and optimize data speed. The use of two or more antennas, along with the transmission of multiple signals (one for each antenna) at the source and the destination, eliminates the trouble caused by multipath wave propagation, and can even take advantage of this effect. Eisha Madhwal 5/30/2012 14
  14. 14.  Some special cases of MIMO are:I. Single Input, Single Output (SISO)II. Single Input, Multiple Output (SIMO)III. Multiple Input, Single Output (MISO) MIMO can also be used with single user or multiple users to form:i. Single-User MIMO (SU-MIMO)ii. Multi-User MIMO (MU-MIMO)iii. Coordinated Multipoint Transmission (CoMP) Eisha Madhwal 5/30/2012 15
  15. 15. Fig. 3: Diagram of MIMO schemes [1] Eisha Madhwal 5/30/2012 16
  16. 16.  MIMO techniques are effective in improving capacity & SE of wireless systems, but on the cost of increased energy consumption. Switching off some radio frequency (RF) amplifiers units at night can save significant energy while maintaining QoS of active users. Adaptive switching between MIMO and SIMO is addressed to save energy at mobile terminals. Eisha Madhwal 5/30/2012 17
  17. 17.  For short range transmission, MISO decreases EE as compared with single antenna transmission if they are not combined with adaptive modulation. By adapting modulation order to balance transmit energy & circuit energy consumption, MISO systems outperform SISO systems. Channel State Information (CSI) helps to adapt the following: Spatial Division Multiplexing Space Time Coding SISO Transmission Eisha Madhwal 5/30/2012 18
  18. 18.  Smart adaptation can achieve better EE-SE trade-off compared with single MIMO mode & the improvement of EE is up to 30% compared with non-adaptive systems. Eisha Madhwal 5/30/2012 19
  19. 19.  Relay transmission technique involves forwarding of information to the local base station (BS) via relay stations installed at different locations to carry out this process. Service coverage and the overall throughput can be enhanced by using this technique. Data from the source (Tx) can be delivered through multiple wireless links to the receiver (Rx). Due to the multiple transmissions, the time to transmit a fixed amount of data reduces and so does the consumed energy. Eisha Madhwal 5/30/2012 20
  20. 20.  In a typical relay system, a transmission period consist of two phases:1. Broadcasting Phase: Source node sends data to the air, which may be received by the relay nodes, or both the relay & the destination nodes.2. Multi-Access Phase: The relay nodes or both the source & relay nodes transmit data to the destination nodes. Eisha Madhwal 5/30/2012 21
  21. 21.  There are basically two types of relay systems: Pure relay systems: The role of the relay nodes is only to help the source node to transmit data. Cooperative relay system: All the nodes act as information sources as well as relays. Eisha Madhwal 5/30/2012 22
  22. 22. Fig. 4: Two structures of Relay system [1] Eisha Madhwal 5/30/2012 23
  23. 23.  The performance of a pure relay system depends upon:i. The transmission strategy of each nodeii. The locations of the relay nodesiii. The data rate used by each node Although power allocation & the no. of locations of nodes affect the EE significantly, such joint design is very complex & may not be suitable for practical scenarios. For simplifying the relay networks, only two hop communications are set up between the source & the destination nodes. Eisha Madhwal 5/30/2012 24
  24. 24. Fig. 5: EE v/s Data Rate in a multi-hop relay system[1] Eisha Madhwal 5/30/2012 25
  25. 25.  Cooperation among users makes it more complex to optimize resource management. It has been studied that the user cooperation can improve user’s EE. Difficulties: Resource at each user should be split for transmitting data both from itself & from other users. Finding an appropriate user as a relay node: It is very complicated to find the optimal partner in a network with a large no. of users (since the no. of possible pairings is huge). Eisha Madhwal 5/30/2012 26
  26. 26.  Besides data streams, signaling symbols are widely used to assist data transmission in wireless communications. The representative are the signaling for synchronization & channel estimation. By gaussian assumption of interference introduced by channel estimation error, it is observed that the EE decreases to zero as the SNR goes to zero, & the maximum EE is achieved at a non-zero SNR value as shown in Fig 6. Eisha Madhwal 5/30/2012 27
  27. 27. Fig 6: EE v/s SNR in the worst case scenario for block fading channels with ‘m’symbol coherence duration & unit variance when the PSD of noise N0=-174dBm/Hz [1] Eisha Madhwal 5/30/2012 28
  28. 28. [1]. Geoffrey Ye Li, Zhikun Xu, Cong Xiong, ChenyangYang, Shunqing Zhang, Yan Chen, and Shugong Xu,“Energy-Efficient Wireless Communications:Tutorial,Survey, and Open Issues”, 2011[2]. Yan Chen, Shunqing Zhang, Shugong Xu, andGeoffrey Ye Li, “Fundamental Tradeoffs on GreenWireless Networks”, 2011[3].[4]., Eisha Madhwal 5/30/2012 29
  29. 29. THANK YOU! Eisha Madhwal 5/30/2012 30