Broadcast Approach to Multiple Access With Local CSIT

Abstract

A two-user multiple access channel is considered, in which the channels undergo slow block fading and the state of each channel is known only to its corresponding transmitter. This paper proposes a novel broadcast strategy for multiple access communication in this channel. In the broadcast approach, in principle, a transmitter with CSI uncertainty sends multiple independent superimposed information layers where the rate of each layer is adapted to a specific channel realization. In the existing broadcast approaches to multiuser communication, the transmitters often directly adopt a single-user strategy and each transmitter adapts its transmission to one unknown channel. The novel aspect of the proposed strategy is that it adapts the designed codebooks to the state of the entire network. This is motivated by the fact that the contribution of each user to the network-wide measures (e.g., capacity region) depends not only on the user's direct channel to the receiver, but also on the qualities of other channels. Average achievable rate region and outer bounds on the capacity region are characterized. Furthermore, the expected capacity region is investigated, where most part of the capacity region boundary is characterized. Finally, an asymptotic capacity region is also characterized.

The Broadcast Approach in Communication Networks

“…Despite the rich literature on the MAC with full CSIT, when the transmitters can acquire only the probability distribution of the fading channel state, without any instantaneous CSIT, the performance limits are not fully known. The broadcast approach is investigated for the two-user MAC with no CSIT in [ 73 , 89 , 90 , 112 , 113 , 114 ]. The multiple access channel is primarily studied in [ 73 , 89 , 90 , 112 , 113 , 114 ].…”

“…The broadcast approach is investigated for the two-user MAC with no CSIT in [ 73 , 89 , 90 , 112 , 113 , 114 ]. The multiple access channel is primarily studied in [ 73 , 89 , 90 , 112 , 113 , 114 ]. Specifically, the effectiveness of a broadcast strategy for multiuser channels is investigated in [ 73 , 90 , 112 ] for the settings in which the transmitters are oblivious to all channels, and in [ 89 , 114 ] for the settings in which each transmitter is oblivious to only channels linking other users to the receiver.…”

“…The multiple access channel is primarily studied in [ 73 , 89 , 90 , 112 , 113 , 114 ]. Specifically, the effectiveness of a broadcast strategy for multiuser channels is investigated in [ 73 , 90 , 112 ] for the settings in which the transmitters are oblivious to all channels, and in [ 89 , 114 ] for the settings in which each transmitter is oblivious to only channels linking other users to the receiver. Specifically, when the transmitters are oblivious to all channels, the approaches in [ 73 ] and [ 112 ] adopt the broadcast strategy designed for single-user channels and directly apply it to the MAC.…”

“…Hence, it proposes a strategy in which the information streams are generated and adapted to the channel’s combined state resulting from incorporating all individual channel states. The setting in which the transmitters have only local CSIT, that is, each transmitter has the CSI of its direct channel to the receiver while being unaware of the states of other users’ channels, is studied in [ 89 , 114 ]. Medium access without transmitter coordination is studied in [ 115 ].…”

Interference Management without CSIT: A Broadcast Approach

“…The transmitter then superimposes and transmits all the generated layers and the receiver decodes as many layers as the actual quality of the channel affords. This approach is then studied under various assumptions for multiple access communications [16]- [21], and for interference channels in [22]- [24]. Specifically, the studies in [22] and [24] adopt superposition coding for opportunistic transmission and decoding of interference, and provide the analysis in the high-SNR regime (generalized degrees of freedom).…”