Performance analysis of two-way relay mixed RF/FSO system with co-channel interference

In this paper,the performance of a two-way relay(TWR)mixed radio frequency/free space optical(RF/FSO)system with co-channel interference(CCI)is investigated.Different from interference-limited one-way relay(OWR)system,CCIs should be considered at both relay and users in TWR system.Additionally,opportunistic user schedule is applied to select the user with the largest signal to interference plus noise ratio(SINR).Exact and asymptotic outage probabil-ity(OP)is derived.Approximate bit error rate(BER)is further presented to evaluate the overall performance.Simula-tion results show that the performance of a TWR system is dominated by the uplink or downlink whose performance is severer.     

物理层安全约束下的AF双向中继系统波束赋形和人工干扰联合设计

波束赋形和人工干扰是现有研究中最为常见的两种物理层安全增强技术,本文针对AF （放大转发）双向中继模型,探讨了两者的联合设计问题。在已知理想信道状态信息的条件下,本文提出了一种波束赋形和人工干扰的混合协同传输方案,推导了总功率受限条件下的和安全速率,通过两步迭代搜索算法得到了其最佳联合方案,并与一种低复杂度的次佳联合方案进行比较。仿真结果验证了所得联合方案优于次佳联合方案,并进一步改善了AF双向中继系统的安全性能。     

On the Secrecy Rate of Limited Feedback Beamforming over Multiple-Input Single-Output Wiretap Channels

The secrecy rate of limited feedback beamforming is studied for a Multiple-Input Single-Output （MISO） wiretap channel with a multi-antenna eavesdropper. We first obtain the secrecy rate of limited feedback beamforming achieved at the legitimate receiver. We then derive a lower bound for the asymptotic secrecy rate in the large system limit, From this bound, we observe a threshold for the ratio of eavesdrop antennas to transmit antennas to obtain a positive secrecy rate. We further show that the secrecy rate loss due to limited feedback decays with the number of feedback bits per transmit antenna.     

On the effect of channel spacing,launch power,and regenerator placement on the design of mixed-line-rate optical networks

Due to the increasing heterogeneity and the growing volume of traffic, telecom backbone networks are going through significant innovations. Wavelength-division multiplexed (WDM) optical networks can now cost-effectively support the growing heterogeneity of traffic demands by having mixed line rates (MLR) over different wavelength channels.The coexistence of wavelength channels with different line rates, e.g., 10/40/100 Gbps, in the same fiber brings up various design issues: in this study, we focus on (1) choice of channel spacing; (2) choice of launch power; and (3) regenerator placement. Channel spacing affects the signal quality in terms of bit-error rate (BER), and hence affects the maximum reach of lightpaths, which is a function of line rates. Various approaches to set an opportunistic width of the channel spacing can be considered, viz., (i) uniform fixed channel spacing specified by the ITU-T grid (typically 50 GHz); (ii) different channel spacing for different line rates; or (iii) optimal value of channel spacing for all line rates that leads to minimum cost.The launch optical power of a signal is another important parameter that affects the network cost. Adjacent channels on different line rates, especially 10 Gbps and 100 Gbps, may exhibit serious degradation of signal quality and optical reach for both the channels due to cross-phase modulation (XPM) between them. Launch power plays a role in such a scenario as it governs the BER by affecting both the signal power and the noise power due to XPM. Moreover, intelligent choice of launch powers on different line rates can significantly reduce the number of regenerators required in the network. The tradeoff between placement of regenerators and choice of launch power is an important problem to address for MLR network design.In this work, we investigate the effects of channel spacing and launch optical power by evaluating the cost of a MLR network for different values of these parameters. We also study the interplay between regenerator placement and launch power. Our results show that (a) it is possible to identify optimal values of channel spacing for a minimum-cost MLR network design, and (b) controlling the power of 10 Gbps and 100 Gbps channels shows maximum sensitivity to the network cost.