Signal Alignment: Enabling Physical Layer Network Coding for MIMO Networking

Signal Alignment: Enabling Physical Layer Network Coding for MIMO Networking

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  Signal Alignment: EnablingPhysical Layer Network Coding for MIMO Networking Mentor: Ms. Alpana Sahu Submitted by: Aishwarya (MAIT, DELHI)
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  INTRODUCTION Two-Way Communication Systems Improvementsof the transmission strategies in the two-way relay channel: from (a) traditional to (b) network coding, and to (c) physical-layer network coding
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  INTRODUCTION Alamouti Scheme • Alamoutidescribed a two-transmitter coding scheme with one or more receivers. • The figure describes two transmit antenna diversity scheme.
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  Block Relaying forPhysical-Layer Network Coding (Two-Way Relay Channels ) • The conventional and logM1(M2)-MA block relaying schemes for the two-way relay systems .
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  Physical Layer NetworkCoding with Signal Alignment Interference Alignment and Cancellation (IAC) • Figure represents 2-client 2-AP MIMO uplink. IAC achieves a throughput of 3 packets per time unit. Each ai is a 2×1 precoding vector. H11a1 is called the direction of x1 at AP1. • Throughput is limited by the number of antennas per AP.
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  Physical Layer NetworkCoding – Signal Alignment (PNC-SA) • PNC-SA simultaneously transmits 4 packets, x1, . . . , x4. Precoding is performed such that at AP1, x1 and x3 are aligned to the same direction, and the same for x2 and x4. • AP1 has two equations and two unknowns (x1+x3, x2+x4), from which it solves x1+x3, x2+x4 further AP2 solves them to recover the 4 original packets, x1, . . . , x4.
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  BER Analysis andComparison • Comparison of the BER performance of PNC-SA and IAC. • For any given modulation, the BER is normally expressed in terms of signal to noise ratio (SNR). BER performance
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  General Degrees ofFreedom of PNC-SA • The DoF of PNC-SA apparently depends on the number of client-AP pairs, as well as the number of antennas each node has. • Figure shows a 3-client 3-AP system with 2 antennas per node (3×3×2 system), where the DoF is 5.
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  PNC-SA with QPSKModulation Constellation diagram for QPSK • Quadrature Phase-Shift Keying (QPSK) is a digital modulation scheme that conveys data by changing the phase of a reference carrier wave. • QPSK modulates by changing the phase of the in-phase (I) carrier from 0◦ to 180◦ and the quadrature-phase (Q) carrier between 90◦ and 270◦. Block diagram of a QPSK transmitter
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  General Applications ofPNC-SA and Packet-Level Throughput • Figure shows the comparison of packet- level throughput achieved by PNC-SA, IAC and MIMO, respectively. • As SNR decreases, the gap between PNC-SA and IAC slightly increases.
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  PNC-SA for InformationExchange • The figure shows the two-way relay channel in a wireless network, where Alice and Bob wish to exchange data packets with the help of a relay. • Each node is equipped with 3 antennas.
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  PNC-SA for CrossUnicasts • Figure depicts two unicast sessions, from S1 to T1 and from S2 to T2, whose routes intersect at a relay. • Each sender cannot directly reach its intended receiver, and needs to resort to the help of the relay node in the middle. PNC-SA with PNC performed at the relay node in the middle
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  The Zig-Zag UnicastFlow: PNC Meets DNC • Here 35, 46 in node represents x3+x5 and x4+x6. The first row transmits 6 packets simultaneously. • The signals are aligned at the second row for demodulating (x5, x6), (x3+x5, x4+x6) and (x1+x3, x2+x4). • In the odd (even) rows, the left-most (right-most) node receive from one sender in the previous row only, without PNC.
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  Multi-Sender Multicast • Figuredepicts a multi-sender multicast in an 8-node MIMO network. • The 3 top nodes are senders, and the 3 bottom nodes are receivers. • Each sender wishes to multicast to all receivers.
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  Cascading SA forMulti-hop Broadcast • In Figure, the sender at the top wishes to broadcast to the entire network, with m rows. • Each node has 2 antennas. The source data is divided into 2 packets, x1 and x2. • We apply normal BPSK instead of PNC demodulation Cascading signal alignment for multi-hop broadcast.
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  Conclusion • PNC-SA, SAcoupled with PNC, can open new design spaces for routing in MIMO wireless networks. • In this, we studied the physical-layer network coding in the two-way relay channels. • In this, we have advocated the use of physical layer network coding (PNC) to improve the network performance in large, general, multi-hop wireless networks. • Studied the detailed PNC-SA scheme design, and conducted BER comparison . • The SNR-BER performance of PNC-SA was analyzed. • Studied the General Applications of PNC-SA and Packet- Level Throughput .
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  References: • S. Zhangand S. C. Liew, “Physical-Layer Network Coding with Multiple Antennas,” in CoRR abs/0910.2603, 2009. • Physical-layer network coding for MIMO systems , By: Ning Xu, B.S., M.S. • S. Zhang, S. C. Liew, and P. P. Lam, “On The Synchronization of Physical-Layer Network Coding,” in Proceedings of IEEE Information Theory Workshop (ITW), 2006. • S. Zhang, S. C. Liew, and P. P. Lam, “Physical-Layer Network Coding,” in Proceedings of ACM MobiCom, 2006.
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  T h an k Y o u ! !