CACH: Cycle-Adjustable Channel hopping for control channel establishment in cognitive radio networks

Abstract

Abstract-Establishing control channels in a cognitive radio network (CRN) is an important and challenging problem. To cope with the problem of control channel saturation and the problem of channel blocking by primary users, channel hopping (CH) schemes are commonly used in the literature for control channel establishment in CRNs. There are three metrics that are widely used for evaluating the performance of CH schemes: (i) degree of overlapping (the number of distinct rendezvous channels), (ii) worst case time-to-rendezvous (TTR), and (iii) system load. In this paper, we focus on the symmetric and synchronous setting and propose a novel Cycle-Adjustable Channel Hopping (CACH) scheme that outperforms several existing CH schemes, including SSCH and QCH, in terms of the three metrics. The key idea of CACH is to create an additional layer of logical channels on the top of physical channels so that the cycle of channel hopping sequences can be adjusted to optimize system performance. The mathematic tools for our scheme are based on the operations in Galois fields that are more general than the prime number modular arithmetic used in SSCH. We show that CACH is much more general than SSCH and it can achieve the maximum degree of overlapping while allowing the worst case TTR to be adjustable. It is also much better than QCH in terms of reducing system load while keeping the same degree of overlapping and the same worst case TTR. Our simulation results show that CACH outperforms several existing schemes in many other aspects, including throughput, and robustness to the disturbance of PUs.

On the Multichannel Rendezvous Problem: Fundamental Limits, Optimal Hopping Sequences, and Bounded Time-to-Rendezvous

“…Clearly, if a finite projective plane of order k exists, then one can select k channels out of the n channels and then use Algorithm 1 to construct random sequences such that the two users are guaranteed to rendezvous within k + 1 steps. (ii) Degree of overlapping: in addition to time-to-rendezvous, another important performance metric is the degree of overlapping that counts the number of distinct channels for the two users to rendezvous [13,47]. For instance, we showed in Theorem 6 that the degree of overlapping for the sequences constructed by Algorithm 3 is n (under the condition of time synchronization), i.e., all the channels can be used for the two users to rendezvous.…”

“…Since finite projective planes can also be used for constructing quorum systems, our construction can be viewed as a better way to map points in finite projective planes to spread out the rendezvous over all channels evenly. In fact, we also proposed CACH in [47] that outperforms QCH in terms of reducing load while keeping the same maximum time-to-rendezvous. (iii) In Section 4, we further take the channel blocking constraint in (A4) into account.…”

基于Galois域的异构认知无线网络信道跳频汇合算法

“…比如文献 [3,4] 利用 quorum 子集系统的轮转闭合性质设计的跳频序列, 能保证在有限时间内汇 合. RCCH 算法 [5] 区分了次用户的收 / 发角色, 要求收发双方跳频序列的初始信道具有相同的奇偶性 而且按照相反的方向进行跳频, 并且限制了信道数为偶数. CHS [6] , CACH [7] 算法与本文都采用 Galois 域的数学工具, 但上述算法仅在时钟同步场景才适用, 对于更为普遍的时钟异步场景便无法保证汇合. 为此很多算法都扩展到时钟异步场景.…”

Fully Distributed Channel-Hopping Algorithms for Rendezvous Setup in Cognitive Multiradio Networks

“…i) Asynchronous local clock. Synchronous algorithms (e.g., CACH [2] and QLCH [3]) assume that SUs are in-sync with each other. However, due to the difficulty in achieving clock synchronization between spatially dispersed SUs, it is thus necessary to support the asynchronous scenario for the rendezvous schemes.…”