Jiancao Hou

Reduced-Complexity Coordinated Beamforming for Multicell Downlink Max–Min SINR Problem

This letter presents a reduced-complexity algorithm for coordinated beamforming aimed at solving the multicell downlink max-min signal-to-interference-plus-noise problem under per-base-station power constraints. It is shown that the proposed algorithm can achieve close performance to the optimum algorithm with faster convergence and lower complexity.

Symbol-level selective decode-forward relaying for uncoordinated dense wireless networks

In this paper, we investigate symbol-level selective decode-forward (SDF) relaying for uncoordinated dense wireless networks. The main objective is to establish reliable communications for such wireless networks, which cannot have accurate link budget allocation due to signalling overhead limitation. To approach this goal, a novel half-duplex absolute difference based symbol-level SDF is developed to enjoy diversity gain at destination node with no signalling between relay and destination node. The proposed selection criteria is designed that no preset threshold is needed at relay, i.e., receive SNR threshold for uncoded systems or LLR threshold for coded systems. Therefore, it is more suitable for the considered uncoordinated dense wireless networks. It offers better performance, in terms of symbol error rate (SER), when compared with the conventional always decode-forward (DF) relaying and frame-level SDF. Computer simulations are carried out to evaluate the proposed approach with respect to the frame length and channel gain. Significant performance improvement is observed in terms of both SER and FER with various setup of frame length and channel gain.

Cooperative Full-Duplex Physical and MAC Layer Design in Asynchronous Cognitive Networks

In asynchronous cognitive networks (CNs), where there is no synchronization between primary users (PUs) and secondary users (SUs), spectrum sensing becomes a challenging task. By combining cooperative spectrum sensing and full-duplex (FD) communications in asynchronous CNs, this paper demonstrates improvements in terms of the average throughput of both PUs and SUs for particular transmission schemes. The average throughputs are derived for SUs and PUs under different FD schemes, levels of residual self-interference, and number of cooperative SUs. In particular, we consider two types of FD schemes, namely, FD transmit-sense-reception (FDr) and FD transmit-sense (FDs). FDr allows SUs to transmit and receive data simultaneously, whereas, in FDs, the SUs continuously sense the channel during the transmission time. This paper shows the respective trade-offs and obtains the optimal scheme based on cooperative FD spectrum sensing. In addition, SUs’ average throughput is analyzed under different primary channel utilization and multichannel sensing schemes. Finally, new FD MAC protocol design is proposed and analyzed for FD cooperative spectrum sensing. We found optimum parameters for our proposed MAC protocol to achieve higher average throughput in certain applications.

Relay-oriented source power allocation for MIMO selective decode-and-forward relaying

For conventional multiple-input and multiple-output (MIMO) selective decode-and-forward (S-DF) relaying network, without global channel knowledge, base station (BS) normally allocates its transmission power for the channel links between itself and its served users. In this case, if the received signal power at relay station (RS) is larger enough, RS will help BS decode and forward the messages. However, such strategy may lose system optimality if BS has the location information of RS. Motivated by this, in this paper, a RS-oriented BS power allocation algorithm for MIMO S-DF relaying is proposed to enhance the system performance. Specifically, BS firstly allocates its transmission power to help as much as data streams to be correctly decoded at RS. Then, if there is still some power left, BS will allocate the residual power for its direct channel links to the users to further increase the system performance. Computer simulations are carried out to examine the proposed scheme in terms of sumrate and bit-error-rate. It is shown that the proposed scheme outperforms the conventional schemes, especially when the RS is placed in the middle of BS and the users.

Error propagation mitigation by exploiting source-relay correlation with limited channel feed-forward bits

In this paper, a complexity-reduced error propagation mitigation algorithm is presented by exploiting source-relay (S-R) correlation information with the limited channel feed-forward bits from the relay node to the destination node. The proposed idea employs the limited channel feed-forward bits as the S-R correlation information indicator and uses it for the iterative decoding at the destination node. Comparing with the conventional threshold-based S-R correlation estimation algorithm, the proposed algorithm can provide close bit error rate performance and omit the iterative S-R correlation estimation process at the destination node. Moreover, the results also show that the proposed algorithm outperforms some of the existing relaying protocols up to 1 dB gain.

Spatial Interweave Opportunistic Spectrum Reuse by Employing Distributed Interference Alignment

Consider spatial interweave opportunistic spectrum reuse scheme, primary user with power constraints maximizes its achievable rate by water-filling its power on singular values of its channel links and leaving some eigen modes free to use. Therefore, secondary user can transmit using this free subspace in order to avoid interference at primary receiver. By employing transmit beamforming, secondary user can design its precoding matrix, where the interference to primary user can be aligned to the free subspace. As a result of non-degraded primary users performance, perfect channel state information (CSI) is required at secondary transmitter. Unfortunately, this kind of CSI is hard to realize, it is therefore in this paper to investigate a limited CSI scheme. By secondary transmitter sensing the label of the Grassmannian quantized channel vectors, the proposed criterion can upper-bound the overall interference at primary receiver with a constant value, which is independent of secondary transmit power. We also study an alternative primary user power allocation strategy in order to balance the overall system performance.