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125
The multi-way relay channel
- in Proc. IEEE Int. Symposium on Inf. Theory (ISIT), Seoul, Korea
"... Abstract—The multi-user communication channel, in which multiple users exchange information with the help of a single relay terminal, called the multi-way relay channel, is considered. In this model, multiple interfering clusters of users communicate simultaneously, where the users within the same c ..."
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Cited by 62 (3 self)
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Abstract—The multi-user communication channel, in which multiple users exchange information with the help of a single relay terminal, called the multi-way relay channel, is considered. In this model, multiple interfering clusters of users communicate simultaneously, where the users within the same cluster wish to exchange messages among themselves. It is assumed that the users cannot receive each other’s signals directly, and hence the relay terminal is the enabler of communication. A relevant metric to study in this scenario is the symmetric rate achievable by all users, which we identify for amplify-and-forward (AF), decodeand-forward (DF) and compress-and-forward (CF) protocols. We also present an upper bound for comparison. The two extreme cases, namely full data exchange, in which every user wants to receive messages of all other users, and pairwise data exchange, consisting of multiple two-way relay channels, are investigated and presented in detail. I.
Two-Unicast Wireless Networks: Characterizing the Degrees-of-Freedom
, 2012
"... We consider two-source two-destination (i.e., two-unicast) multi-hop wireless networks that have a layered struc-ture with arbitrary connectivity. We show that, if the channel gains are chosen independently according to continuous distribu-tions, then, with probability 1, two-unicast layered Gaussi ..."
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Cited by 34 (9 self)
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We consider two-source two-destination (i.e., two-unicast) multi-hop wireless networks that have a layered struc-ture with arbitrary connectivity. We show that, if the channel gains are chosen independently according to continuous distribu-tions, then, with probability 1, two-unicast layered Gaussian net-works can only have 1, 3/2 or 2 sum degrees-of-freedom (unless both source-destination pairs are disconnected, in which case no degrees-of-freedom can be achieved). We provide sufficient and necessary conditions for each case based on network connectivity and a new notion of source-destination paths with manageable interference. Our achievability scheme is based on forwarding the received signals at all nodes, except for a small fraction of them in at most two key layers. Hence, we effectively create a “condensed network” that has at most four layers (including the sources layer and the destinations layer). We design the transmission strategies based on the structure of this condensed network. The converse results are obtained by developing information-theoretic inequalities that capture the structures of the network connectivity. Finally, we extend this result and characterize the full degrees-of-freedom region of two-unicast layered wireless networks.
JMB: Scaling Wireless Capacity with User Demands
"... We present joint multi-user beamforming (JMB), a system that enables independent access points (APs) to beamform their signals, and communicate with their clients on the same channel as if they were one large MIMO transmitter. The key enabling technology behind JMB is a new low-overhead technique fo ..."
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Cited by 30 (3 self)
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We present joint multi-user beamforming (JMB), a system that enables independent access points (APs) to beamform their signals, and communicate with their clients on the same channel as if they were one large MIMO transmitter. The key enabling technology behind JMB is a new low-overhead technique for synchronizing the phase of multiple transmitters in a distributed manner. The design allows a wireless LAN to scale its throughput by continually adding more APs on the same channel. JMB is implemented and tested with both software radio clients and off-the-shelf 802.11n cards, and evaluated in a dense congested deployment resembling a conference room. Results from a 10-AP software-radio testbed show a linear increase in network throughput with a median gain of 8.1 to 9.4×. Our results also demonstrate that JMB’s joint multi-user beamforming can provide throughput gains with unmodified 802.11n cards.
Multiple access channels with states causally known at transmitters,” November 2010, submitted to IEEE Transactions on Information Theory, available online at http://arxiv.org/abs/1011.6639
"... Abstract—It has been recently shown by Lapidoth and Steinberg that strictly causal state information can be beneficial in multiple access channels (MACs). Specifically, it was proved that the capacity region of a two-user MAC with independent states, each known strictly causally to one encoder, can ..."
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Cited by 21 (3 self)
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Abstract—It has been recently shown by Lapidoth and Steinberg that strictly causal state information can be beneficial in multiple access channels (MACs). Specifically, it was proved that the capacity region of a two-user MAC with independent states, each known strictly causally to one encoder, can be enlarged by letting the encoders send compressed past state information to the decoder. In this study, a generalization of the said strategy is proposed whereby the encoders compress also the past transmitted codewords along with the past state sequences. The proposed scheme uses a combination of long-message encoding, compression of the past state sequences and codewords without binning, and joint decoding over all transmission blocks. The proposed strategy has been recently shown by Lapidoth and Steinbergtostrictlyimprove upon the original one. Capacity results are then derived for a class of channels that include two-user modulo-additive state-dependent MACs. Moreover, the proposed scheme is extended to state-dependent MACs with an arbitrary number of users. Finally, output feedback is introduced and an example is provided to illustrate the interplay between feedback and availability of strictly causal state information in enlarging the capacity region. Index Terms—Long-message encoding, multiple access channels (MACs), output feedback, quantize-forward, state-dependent channels, strictly causal state information. I.
Degrees of freedom of two-hop wireless networks: Everyone gets the entire cake
- IEEE Trans. Inf. Theory
, 2014
"... Abstract—We show that fully connected two-hop wireless networks with K sources, K relays and K destinations have K degrees of freedom for almost all values of constant channel coefficients. Our main contribution is a new interference-alignment-based achievability scheme which we call aligned network ..."
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Cited by 19 (1 self)
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Abstract—We show that fully connected two-hop wireless networks with K sources, K relays and K destinations have K degrees of freedom for almost all values of constant channel coefficients. Our main contribution is a new interference-alignment-based achievability scheme which we call aligned network diagonalization. This scheme allows the data streams transmitted by the sources to undergo a diagonal linear transfor-mation from the sources to the destinations, thus being received free of interference by their intended destination. I.
On the optimal compressions in the compressand-forward relay schemes
- IEEE Trans. Inf. Theory
, 2013
"... Abstract—In the classical compress-and-forward relay scheme developed by Cover and El Gamal, the decoding process operates in a successive way: the destination first decodes the compression of the relay’s observation and then decodes the original message of the source. Recently, several modified com ..."
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Cited by 18 (1 self)
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Abstract—In the classical compress-and-forward relay scheme developed by Cover and El Gamal, the decoding process operates in a successive way: the destination first decodes the compression of the relay’s observation and then decodes the original message of the source. Recently, several modified compress-and-forward relay schemes were proposed, where the destination jointly decodes the compression and the message, instead of successively. Such a mod-ification on the decoding process was motivated by realizing that it is generally easier to decode the compression jointly with the orig-inal message, and more importantly, the original message can be decoded even without completely decoding the compression. Thus, joint decoding provides more freedom in choosing the compres-sion at the relay. However, the question remains in these modi-fied compress-and-forward relay schemes—whether this freedom of selecting the compression necessarily improves the achievable
Multiple-input multiple-output two-way relaying: A space-division approach
- IEEE TRANS. INF. THEORY
, 2013
"... We propose a novel space-division-based net-work-coding scheme for multiple-input multiple-output (MIMO) two-way relay channels (TWRCs), in which two multiantenna users exchange information via a multiantenna relay. In the proposed scheme, the overall signal space at the relay is divided into two s ..."
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Cited by 16 (11 self)
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We propose a novel space-division-based net-work-coding scheme for multiple-input multiple-output (MIMO) two-way relay channels (TWRCs), in which two multiantenna users exchange information via a multiantenna relay. In the proposed scheme, the overall signal space at the relay is divided into two subspaces. In one subspace, the spatial streams of the two users have nearly orthogonal directions and are completely decoded at the relay. In the other subspace, the signal direc-tions of the two users are nearly parallel, and linear functions of the spatial streams are computed at the relay, following the principle of physical-layer network coding. Based on the recov-ered messages and message-functions, the relay generates and forwards network-coded messages to the two users. We show that, at high signal-to-noise ratio, the proposed scheme achieves the asymptotic sum-rate capacity of the MIMO TWRC within bits per user-antenna, for any antenna con-figuration and any channel realization. We perform large-system analysis to derive the average sum-rate of the proposed scheme over Rayleigh-fading MIMO TWRCs. We show that the average asymptotic sum-rate gap to the capacity is at most 0.053 bits per relay-antenna. It is demonstrated that the proposed scheme significantly outperforms the existing schemes.
MegaMIMO: Scaling Wireless Capacity with User Demands
"... We present MegaMIMO, a joint multi-user beamforming system that enables independent access points (APs) to beamform their signals, and communicate with their clients on the same channel as if they were one large MIMO transmitter. The key enabling technology behind MegaMIMO is a new low-overhead tech ..."
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Cited by 15 (7 self)
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We present MegaMIMO, a joint multi-user beamforming system that enables independent access points (APs) to beamform their signals, and communicate with their clients on the same channel as if they were one large MIMO transmitter. The key enabling technology behind MegaMIMO is a new low-overhead technique for synchronizing the phase of multiple transmitters in a distributed manner. The design allows a wireless LAN to scale its throughput by continually adding more APs on the same channel. MegaMIMO is implemented and tested with both software radio clients and off-the-shelf 802.11n cards, and evaluated in a dense congested deployment resembling a conference room. Results from a 10-AP software-radio testbed show a linear increase in network throughput with a median gain of 8.1 to 9.4×. Our results also demonstrate that MegaMIMO’s joint multi-user beamforming can provide throughput gains with unmodified 802.11n cards.
Short-message quantize-forward network coding
- in 8th Int’l Workshop on Multi-Carrier Systems Solutions (MC-SS
, 2011
"... Abstract—Recent work for single-relay channels shows that quantize-forward (QF) with long-message encoding achieves the same reliable rates as compress-forward (CF) with short-message encoding. It is shown that short-message QF with backward or pipelined (sliding-window) decoding also achieves the s ..."
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Cited by 13 (1 self)
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Abstract—Recent work for single-relay channels shows that quantize-forward (QF) with long-message encoding achieves the same reliable rates as compress-forward (CF) with short-message encoding. It is shown that short-message QF with backward or pipelined (sliding-window) decoding also achieves the same rates. Similarly, for many relays and sources, short-message QF with backward decoding achieves the same rates as long-message QF. Several practical advantages of short-message encoding are pointed out, e.g., reduced delay and simpler modulation. Fur-thermore, short-message encoding lets relays use decode-forward (DF) if their channel quality is good, thereby enabling multi-input, multi-output (MIMO) gains that are not possible with long-message encoding. Finally, one may combine the advantages of long- and short-message encoding by hashing a long message to short messages. I.
Uplink Multicell Processing with Limited Backhaul via Per-Base-Station Successive Interference Cancellation
"... Abstract—This paper studies an uplink multicell joint process-ing model in which the base-stations are connected to a central-ized processing server via rate-limited digital backhaul links. We propose a simple scheme that performs Wyner-Ziv compress-and-forward relaying on a per-base-station basis f ..."
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Cited by 12 (1 self)
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Abstract—This paper studies an uplink multicell joint process-ing model in which the base-stations are connected to a central-ized processing server via rate-limited digital backhaul links. We propose a simple scheme that performs Wyner-Ziv compress-and-forward relaying on a per-base-station basis followed by successive interference cancellation (SIC) at the central processor. The proposed scheme has a significantly reduced complexity as compared to joint decoding, resulting in an easily computable achievable rate region. Although suboptimal in general, this paper shows that the proposed per-base-station SIC scheme can achieve the sum capacity of a special Wyner cellular model to within a constant gap. This paper also establishes that in order to achieve to within a constant gap to the maximum SIC rate with infinite backhaul, the limited-backhaul system must have backhaul capacities that scale logarithmically with the signal-to-interference-and-noise ratios (SINRs) at the base-stations. Further, this paper studies the optimal backhaul rate allocation problem for the per-base-station SIC model with a total backhaul capacity constraint, and shows that the sum-rate maximizing allocation should also have individual backhaul rates that scale logarithmically with the SINR at each base-station. Finally, the proposed per-base-station SIC scheme is evaluated in a practical multicell network to quantify the performance gain brought by multicell processing. Index Terms—Coordinated multi-point (CoMP), interference channel, limited backhaul network multiple-input multiple-output (MIMO), relay channel, successive interference cancel-lation, Wyner-Ziv coding I.
