Time-Asynchronous Robust Cooperative Transmission for the Downlink of C-RAN

Abstract

This work studies the robust design of downlink precoding for cloud radio access network (C-RAN) in the presence of asynchronism among remote radio heads (RRHs). Specifically, a C-RAN downlink system is considered in which non-ideal fronthaul links connecting two RRHs to a Baseband Unit (BBU) may cause a time offset, as well as a phase offset, between the transmissions of the two RRHs. The offsets are a priori not known to the BBU. With the aim of counteracting the unknown time offset, a robust precoding scheme is considered that is based on the idea of correlating the signal transmitted by one RRH with a number of delayed versions of the signal transmitted by the other RRH. For this transmission strategy, the problem of maximizing the worst-case minimum rate is tackled while satisfying per-RRH transmit power constraints. Numerical results are reported that verify the advantages of the proposed robust scheme as compared to conventional non-robust design criteria as well as non-cooperative transmission.

Interference mitigation and receiving performance improvement strategies for local cooperation in the 5G system

“…It is evident that r n l n v is a variable and the number of its possible values is 2 M . Based on (11) and modulation mode, the BER for stream l n can be analysed. For instance, the BER for stream l n with PSK mode is given as [36]…”

“…Φ n(a) = arg min tr Φ n(a) Second, some information interaction between the nodes is necessary in (11). However, node i independently calculates the possible values of f n i δ n l n i , and then shares the calculated numbers.…”

“…Then, we select the largest value and set the relevant results as the final transmitters. Observe (24) and (11), it is easier to obtain the ASNR. However, from (12) and (13), we notice that the relation between SNR and BER is non-linear.…”

“…This flexibility mainly reflects on the equal and unequal assignment rules. Specifically, in (11), the average power p n l n can be shown as…”

“…As we see, compared to other wireless communication systems, because the processing ability of each 5G network is evidently more powerful, it can apply the globally cooperative style (e.g. C-RAN [11,12]). Through this style, the network can integrate all resources and exploit these resources to achieve different schemes.…”