MIMO Evolution: Coordinated Multi Point Transmission / reception (COMP)
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The Presentation Video https://www.youtube.com/watch?v=5GiiIppb2o4&feature=youtu.be *Contents 1-Challenges in Wireless Communication 2-Multipath andFading 3-MIMO and Diversity 4-Receive Diversity /Maximum ratio combining (MRC) 5-MIMO Evolution 6- Coordinated Multi point (CoMP) 7-Level of Cooperation and Architecture 8-CoMP System Model
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MIMO Evolution: Coordinated Multi Point Transmission / reception (COMP)
- 1. By Mohamed Aref Teaching Assistant Electrical Engineering Dept., Suez Canal University Email: mattia@eng.suez.edu.eg
- 2. Challenges in Wireless Communication 2 Multipath and Fading MIMO and Diversity Receive Diversity /Maximum ratio combining (MRC) Alamouti Space Time Block Coding Scheme MIMO Evolution Coordinated Multi point (CoMP) Level of Cooperation and Architecture CoMP System Model
- 3. High data rate demand Lightweight and simple remote terminals Mobility and portability Interference and noise Quality of service QoS Security and Privacy 3
- 4. Line of sight LOS Reflection Scattering Diffraction Rx anntena Tx anntena 4
- 5. 5 Bc :Coherence bandwidth s(t) t s(t) t s(t) t s(t) t Destructive interference Constructive Interference 5
- 7. 7
- 8. 8 8 Frequency selective Time variance
- 9. 9 •Frequency diversity •Time Diversity •Polarization Diversity •Space Diversity Diversity Types •Multiplexing •Beamforming MIMO Functions
- 11. 11 Select the highest power gain branch. 11
- 12. 12 threshold Ant. Sw. Switch to the max power gain antenna when the current one falls below a given threshold. 12
- 13. 13 2211 rhrhZ 21 ararZ Each signal branch weighted with the same factor, irrespective of the signal amplitude. Each signal branch is multiplied by a weight factor that is proportional to the signal amplitude. 13
- 14. 14 Maximum likelihood detector 1h 2h 1 ˆs Channel estimator Channel estimator 1r 2Rx 2n1n 1Tx 1s 2r 1Rx ** 1111 nshr Received signals Receiver Combining scheme Transmit symbols 1s 2122 nshr 1 ~s 22111 2 2 2 1 22111 )( ~ nhnhshh rhrhs )( ~ ˆ 2 2 2 1 1 1 hh s s Detector 1h 2h 1 11 j ehh 2 22 j ehh Interference and noise 14
- 15. 122111 nshshr 212212 nshshr 22111 ~ rhrhs 21122 ~ rhrhs t Tt 1s 2s * 2s * 1s 1Tx 2Tx time antennas Alamouti Encoding Received signals Alamouti Decoding Transmit symbols 21,ss Combiner Detector Channel estimator 1Tx 2Tx 2r 1s 2s * 2s * 1s 1h 2h 1r 1n 2n 2h1h 1h 2h 1 ~s 2 ~s xR 1 ˆs 2 ˆs 15
- 16. Detector 2h1h 1 ~s 2 ~s 1 ˆs 2 ˆs 22111 2 2 2 1 22111 )( ~ nhnhshh rhrhs 12212 2 2 2 1 21122 )( ~ nhnhshh rhrhs )( ~ ˆ 2 2 2 1 1 1 hh s s )( ~ ˆ 2 2 2 1 2 2 hh s s Detector 1 6 16
- 17. 0 2 4 6 8 10 12 14 16 18 20 10 -4 10 -3 10 -2 10 -1 10 0 Eb/No (dB) BER Transmit vs. Receive Diversity No Diversity (1Tx, 1Rx) Alamouti (2Tx, 1Rx) Maximal-Ratio Combining (1Tx, 2Rx) 3 dB • The performance of Alamouti scheme with two transmitters and a single receiver is 3 dB worse than two-branch MRRC. • Each transmit antenna radiates half the energy in order to ensure the same total radiated power as with one transmit antenna. 17
- 18. 1122111111 nshshr 1212121112 nshshr 22222112122111111 ~ rhrhrhrhs 22122122121111212 ~ rhrhrhrhs t Tt 1s 2s * 2s * 1s 1Tx 2Tx time antennas Alamouti Encoding Received signals Alamouti Decoding Transmit symbols 21,ss 1Rx 2Rx 2122211221 nshshr 2212221222 nshshr Combiner Detector Channel estimator 1Tx 2Tx 1s 2s * 2s * 1s 11r 21n 12h11h 11h 12h 1 ~s 2 ~s 2Rx Channel estimator 22h21h 22n 11n 12n 11h 12h 21h 21h 22h 22h 2 ˆs1 ˆs 12r 21r 22r 1 8 18
- 20. • The Alamouti scheme provides similar performance to MRC regardless of the employed coding and modulation schemes. • The scheme does not require any feedback from the receiver to the transmitter and its computation complexity is similar to MRC. •No bandwidth expansion needed, as the redundancy added in space. • The scheme can easily be generalized to 2 transmit antennas and M receive antennas to provide diversity order of 2M. • Alamouti schemes is the basic for what is called STBC. • An extension for the STBC is the OSTBC which is widely used (e.g. LTE). 20
- 22. •In conventional wireless cellular systems, signal processing is performed in each cell independently; out-of-cell interference is treated as background noise. •Base stations from different cells communicate with their respective remote terminals only. BS1BS2 UE1 22
- 23. •That inter-cell interference can be seen as another resource if base stations cooperatively process signals. Thus interference may be exploited, or coordinated, instead of removing it. BS1BS2 UE1 •Such techniques are often referred to as virtual MIMO, network MIMO, Cooperative MIMO, Multi- Cell MIMO, or more recently, Coordinated Multi-Point (CoMP). 23
- 24. •The main idea of CoMP is as follows: when a UE is in the cell-edge region, it may be able to receive signals from multiple cell sites and the UE’s transmission may be received at multiple cell sites regardless of the system load. •Base stations no longer tune separately their physical and link/MAC layer parameters (power level, time slot, subcarrier usage, beamforming coefficients etc.) or decode independently of one another, but instead coordinate their coding or decoding operations on the basis of global channel state and user data information exchanged over backhaul links among several cells. 24
- 25. •The transmission to a single scheduled UE is performed by a unique BS (each UE receives the data from its serving BS). •However; the scheduling, including any transmission weights, is dynamically coordinated between the BSs in order to control and/or reduce the unnecessary interference between different transmissions. •In principle, the best serving set of UEs will be selected so that the transmitter beams are constructed to reduce the interference on other UEs, while increasing the served UE’s signal strength. 25
- 26. •The data is simultaneously transmitted from multiple BS to each UE. •So, the multi-point transmissions will be coordinated as a single transmitter with antennas that are geographically separated. •JP requires the exchange of UE data among BSs as well as UE channel information and consequently, requires significant backhaul resources. 26
- 27. •UE sends back its estimated and quantized channel state information (CSI) to all the cooperative BSs through individual feedback links. •Each BS unilaterally optimizes the linear precoding matrix, based on its gathered global CSI. 27
- 28. •UE estimates the channel state information (CSI) of all cooperating BSs, quantizes it and sends to its anchor BS. • The quantized CSI received at each individual BS is reported to the Central Unit (CU). •The CU jointly performs linear precoding and sends back the precoding matrices to each BS. 28
- 29. •One fundamental challenge facing CoMP is the large network infrastructure required between cooperating base stations, typically referred to as backhaul. •Introducing cooperation between base stations can easily lead to yet another n-fold increase of backhaul infrastructure unless smart and backhaul-efficient cooperation techniques are employed. •CoMP was introduced mainly for the cell-edge users, therefore it is expected that these users should take more in the backhaul than the cell center users. 29
- 30. •For CoMP model, the CS and JP schemes are based on the use of the SINR as the performance metric that needs to be maximized in order to increase the overall cell throughput. •Let 𝑁 cells and 𝐾 users per cell with 𝑁𝑡 antennas at each base-station. antenna at each remote user. •Let Si be a complex scalar denoting the information signal for the i th user, Wi be its associated beamforming vector, and Hi the channel vector from the cell to i th user. 30
- 31. •The signal-to interference- plus-noise ratio (SINR) at the input of the receiver(i th user) is given by: 0 / 2 i 2 i i |||| |||| SINR NHw Hw ik k i Interference from other base stations Noise Desired power from the serving BS 31
- 32. 32
- 33. • Leakage refers to the interference caused by the signal intended for a desired UE on the remaining UEs. That is, leakage is a measure of how much signal power leaks into the other UEs. 33
- 34. •The performance criterion for choosing the precoding/beamforming weighting vectors will be based on maximizing SLNR for all UEs. •The leakage-based precoding/beamforming leads to a decoupled optimization problem and admits an analytical closed form solution. •The SLNR at the i th UE over can be expressed as: 34
- 36. •S. M. Alamouti, “A simple transmitter diversity scheme for wireless communications,” IEEE J. Select. Areas Commun., Oct. 1998, vol. 16, pp.1451–1458. •Jerry R. Hampton, “Introduction to MIMO Communications”, Cambridge University Press, 2014. •R. Irmer, H. Droste, P. Marsch, M. Grieger, G. Fettweis, S. Brueck, H.-P. Mayer, L. Thiele, and V. Jungnickel, “Coordinated multipoint: Concepts, performance, and field trial results,” IEEE Communications Magazine, vol. 49, no. 2, pp. 102 – 111, feb 2011. •N. Seifi, M. Viberg, J. Robert W. Heath, J. Zhang, and M. Coldrey,“Coordinated single-cell vs multi-cell transmission with limited-capacity backhaul,” in Proc. IEEE Asilomar Conf. on Signals, Syst. and Comput.,Nov. 2010. •Musa Ali Abu-Rgheff, “Introduction to CDMA Wireless Communications”, Academic Press, 2007. •Hamid Jafakhani, “Space-Time Coding Theory and Practice”, Cambridge University Press, 2005. •Vigay K. Garg, “Wireless Communications and Networking”, Elsevier Inc., 2007. •Yong Soo Cho, Jaekwon Kim, “MIMO-OFDM wireless communications with MATLAB”, John Wiley & Sons (Asia) Pte Ltd, 2010. •Other internet resources. 36