Hang Long

Performance analysis for downlink massive MIMO system with ZF precoding

This paper investigates the performance for the downlink massive multiple-input multiple-output system when the base station serves multiple user terminals UTs using zero-forcing precoding. The tight lower bound of average area spectrum efficiency A2SE is derived as a function of the number of transmission antennas, the number of UTs and the equivalent transmission signal-to-noise ratio. Regarding the lower bound as the approximate A2SE, the optimal number of UTs maximising the A2SE is attained for given the number of transmission antennas and the equivalent transmission signal-to-noise ratio. After formulating the realistic power consumption model in consideration of both the transmission power and circuit power, the trade-off between energy efficiency EE and A2SE is established, and the optimal EE with respect to A2SE is deduced. Moreover, both the outage probability and bit error ratio expressions are derived related to the degrees of freedom, defined as the difference between the number of transmission antennas and the number of UTs. Simulation results coincide to the analysis well, and they indicate that deploying more transmission antennas or multiplexing a rational number of UTs can improve the A2SE and EE, increasing the degrees of freedom will better both the outage probability and bit error ratio. Copyright

Secrecy Capacity Enhancement With Distributed Precoding in Multirelay Wiretap Systems

The secrecy capacity of relay communications is investigated in this paper, where an eavesdropper is present. Distributed precoding through multiple relay nodes can be used to enhance the received signal power at the destination node and to mitigate the signal leakage to the eavesdropper, simultaneously. Due to individual power constraints at relay nodes, the distributed precoding scalar at each relay node is equivalent to a distributed precoding angle. An iterative algorithm is proposed to find the suboptimum distributed precoding angles at all the relay nodes, where the channel state information (CSI) sharing overhead among the relay nodes can also be substantially reduced. Each relay node receives the equivalent CSI from its preceding relay node, computes its distributed precoding angle, and updates the equivalent CSI for the next relay node. Compared with the simple decode-and-forward relaying protocol with random distributed precoding, the proposed iterative distributed precoding algorithm is able to further improve on the secrecy capacity of the multirelay wiretap system with an acceptable CSI sharing overhead.

Cooperative jamming and power allocation with untrusty two-way relay nodes

This study investigates the security of the two-way relaying system with untrusty relay nodes. Cooperative jamming schemes are considered for bi-directional secrecy communications. The transmit power of each source node is divided into two parts corresponding to the user and jamming signals, respectively. Two different assumptions of the jamming signals are considered. When the jamming signals are a priori known at the two source nodes, closed-form power allocation expressions at two source nodes are derived. Under the assumption of unknown jamming signals, it is proven that the cooperative jamming is useless for the system secrecy capacity, because that all the power should be allocated to the user signals at each source node. Relay selection is also investigated based on the analysis of cooperative jamming. Simulation results are presented to compare the system secrecy capacities under the two jamming signal assumptions.

Proportional Fair Resource Partition for LTE-Advanced Networks with Type I Relay Nodes

In 3GPP LTE-Advanced networks deployed with type I relay nodes (RNs), resource partition is required to support in-band relaying. This paper focuses on how to partition system resources in order to attain improved fairness and efficiency. We first formulate the generalized proportional fair (GPF) resource allocation problem to provide fairness for all users served by the evolved node B (eNB) and its subordinate RNs. Assuming traditional proportional fair scheduling is executed independently at the eNB and each RN to achieve local fairness, we propose the proportional fair resource partition algorithm to tackle the GPF problem and ensure global fairness. Through system level simulations, the proposed algorithm is evaluated and compared with both non-relaying and relaying systems with the fixed resource partition approach. Simulation results demonstrate that the proposed algorithm can achieve a good trade-off between system throughput and fairness performance.

Tabu Search Detection for MIMO Systems

In this paper, tabu search (TS) is applied to the detection algorithm of MIMO system, which is originally designed to find the approximate solution of combinatorial optimization problems. Resorting to an original two embedded cubes stereograph, we give a simple illustration of TS process. As a simple add-on to traditional suboptimal detectors, TS provides the potential of moving toward the best ML solution. The method of skipping out of the search under a certain condition in advance is proposed, leading to the flexible tradeoff between the performance and the complexity. Simulation results show that the advantage of TS detection on performance comparing with the traditional detection is great, especially when the system has more transmit-antennas.

Performance and Analysis on LTE System under Adjacent Channel Interference of Broadcasting System

In the progress of the standardization of the long term evolution (LTE) system, the interference between the LTE system and other systems is quite important. In China, the LTE system and the broadcasting system may deploy in the same geographical area in adjacent frequency channels around the band of 698 MHz in digital dividend spectrum, which is free up for the conversion from analog TV to digital TV. Therefore, with the deployment of frequency planning, it is urgent to ensure the coexistence between the LTE system and the broadcasting system. This paper is aiming at analyzing the interference from the broadcasting system to the LTE system with different distances between the two systems and different offset distances with Monte Carlo simulations. We calculate the required adjacent channel interference ratio values to achieve 5% throughput loss. Simulation results show that the interference situation of LTE uplink is much more severe than LTE downlink and should be paid more attention. Additionally, it can be improved by locating the broadcasting system transmitter at the LTE systems cell edge.

Cooperative jamming and power allocation in three-phase two-way relaying wiretap systems

The security of the three-phase two-way relaying system with an eavesdropper is investigated in this paper. A cooperative jamming and power allocation scheme is proposed to enhance the system secrecy capacity. When a source node transmits user signals to the relay node, the other source node interferes the relay node with pre-defined jamming signals simultaneously. Optimum power allocation between the user and jamming signals at each source node is analyzed. Our analytical results suggest that the proposed cooperative jamming scheme improves on the system secrecy capacity, especially when the channel gains of the two source-relay links are of large difference. Simulation results in close agreement with analytical results clearly demonstrate the advantage of the proposed cooperative jamming scheme.

Performance analysis of the unicasting mode in multi-relay systems

The unicasting mode is a natural choice in multi-relay systems to utilize the spatial potential of source and destination nodes. In the unicasting phase, the source node transmits different data streams to several relay nodes with the downlink multi-user precoding; in the multi-accessing phase, relay nodes transmit the received data streams to the destination node simultaneously. In this paper, the received signal-to-noise-ratio (SNR) at the destination node of the unicasting mode is analyzed and derived, which can be calculated with two SNRs related to the two phases as an approximate harmonic mean function. Then, an approximate method for calculating the system ergodic capacity is presented. The inner products between singular vectors are approximately replaced by their expectations and distribution functions of singular values are derived. The numerical and simulation results demonstrate the efficiency of the analysis and the approximate method. Copyright

Performance analysis for downlink massive multiple-input multiple-output system with channel state information delay under maximum ratio transmission precoding

This study comprehensively investigates the performance of the downlink massive multiple-input multiple-output (MIMO) system with channel state information (CSI) delay, when the base station serves multiple user terminals (UTs) taking advantage of maximum ratio transmission precoding. Through the characteristic analysis of the received signal-to-interference-plus-noise ratio at UT, the tight lower bound of average area spectrum efficiency (SE) and its asymptotic bound with the infinite number of UTs are deduced, respectively. Based on the asymptotic bound and the realistic power consumption model consisting of both radiated power and circuit power, the trade-off between SE and energy efficiency (EE) is developed, and the optimal EE with respect to SE is attained concisely. Moreover, the approximate expressions of both outage probability and bit error ratio (BER) are derived when the massive MIMO system works at its interference limited region. All theoretical results coincide to numerical results, and they show that deploying more transmission antennas will be helpful to improve SE, EE and reliability simultaneously; SE will be enhanced; however, the reliability, including both outage probability and BER, will be worsened by multiplexing more UTs; enlarging CSI delay can extensively deteriorate SE, EE and reliability.

Analysis of Conditional Error Rate and Combining Schemes in HARQ

In hybrid automatic repeat request (HARQ), maximum ratio combining (MRC) is usually employed at the receiver if the retransmission signal is the same as that in the first transmission. However, conventional performance analysis of HARQ and MRC does not consider that all previous transmissions fail. In this paper, we analyze the conditional error rate of HARQ with arbitrary combining schemes. Both the theoretical and approximate expressions of the conditional error rate are derived. Our analytical and simulation results reveal that conventional MRC is not optimum for HARQ, especially when the packet is short or the channel gain of the first transmission is much better than that of retransmission.