To improve the transmission performance of two-way wireless relay networks (TWRNs), the present paper proposes a novel transmission scheme based on the techniques of decode-and-forward (DF) and network coding (NC). To our best knowledge, the proposed scheme is the first known one that can support two end users in a TWRN with an arbitrary number of relays to exchange two data packets every three timeslots and can achieve a better spectrum efficiency than the existing schemes of the same style. Moreover, we also propose an error control scheme for each node in a TWRN to retransmit its erroneous data packets appropriately such that any transmission error will not be propagated throughout the whole TWRN. Numerical simulation also shows that the proposed schemes outperform the existing ones in terms of average transmission throughput.

To improve the efficiency of blind rendezvous among multi-radio asynchronous cognitive users (CUs), this paper proposes to construct a common set of CH sequences at different computational complexity for guiding the multiple radios of each CU to perform channel hopping (CH). The main advantages of this construction include its approaching to the theoretical lower bound on the time-to-rendezvous of multi-radio asynchronous CH systems closely when any two CUs have only one commonly available channel due to the interference from primary users (PUs) and its effective reduction of the same metric when no PU interference exists. Numerical simulation also shows that, compared with the existing multi-radio asynchronous CH systems, the proposed CH sequences incur a shorter rendezvous delay under different numbers of radios or rendezvous channels.

In order for cognitive radio networks (CRNs) to exchange control information reliably and efficiently, this paper proposes a novel channel hopping (CH) scheme, namely DS-ACH, for cognitive users (CUs) without a synchronized time clock to achieve rendezvous in the blind fashion. Originating from the mathematical concept of relaxed cyclic difference set (DS), the proposed DS-ACH can guarantee any two CUs to always rendezvous in every timeslot and at an arbitrary number of channels without knowing their time clock offset and CH sequences. Moreover, we show that the DS-ACH constructed based on a special class of DSs can closely approach the theoretical lower bound on the number of radio transceivers for asynchronous CUs to rendezvous blindly in every timeslot and hence minimize their required hardware complexity for exchanging control information at the minimum time delay. Numerical simulation also shows that the proposed asynchronous CH scheme outperforms the existing ones in several key performance metrics of CRNs.

A fibre memory is a serial connection of fibre‐switch blocks , each combining fibre delay lines with one optical switch. With enhanced flexibility in processing fluid optical data, fibre memories allow ramified applications in the existing literature. This study concentrates on the implementations of timeslot interchangers (TSIs) by fibre memories based on a special type of low‐complexity switches, called rotators , under periodic switching control. The proposed TSI structure achieves an economic tradeoff between control and component complexities in the construction of large‐scale optical TSIs.

Scheduling algorithms are crucial for most existing switches to improve the throughput. However, the delay of the switching fabric cannot be guaranteed with such scheduling algorithms. This paper aims to design a novel load-balanced wire-speed multicast switching fabric along with the attractive merits of network coding. We adopt a two-phase self-routing switching fabric constructed by Boolean-multicast concentrators (SRBMCs), where the first SRBMC distributes the incoming cells to its outputs uniformly and the second allows the distributed cells to be self-routed and multicast to their destinations concurrently. To further improve the switching performance, linear network coding is smoothly combined with SRBMC to reduce the packet loss rate. Theoretical analysis and numerical simulation demonstrate that the proposed switching fabric cannot only achieve wire-speed multicast switching but also be recursively constructed into an indefinite large-scale one with such merits as no internal buffers, low complexity, and guarantee in switching delay. Finally, we implement the proposed fabric on Field-Programmable Gate Array and verify its performance in multicast switching.

Spectrum leasing has been widely regarded as one of the most effective ways to improve the utilization of limited spectrum resources. The existing literatures normally regulate secondary users (SUs) to lease unused licensed spectrum from primary users (PUs) for indefinite or predetermined time length, which does not adapt to real-time traffic demands of SUs and may limit the utilization of licensed spectrum channels. In view of this, the present paper proposes a novel traffic-adaptive spectrum leasing scheme, which allows PUs and SUs to negotiate leasing periods with variable time length such that SUs can continuously utilize the leasing channels for transmitting dynamically generated secondary packets until their transmission buffers become empty. Following this scheme, we further formulate the utilities of both PUs and SUs in traffic-adaptive spectrum leasing based on M/M/k queues and derive the unique sub-game perfect equilibrium of this scheme based on the Stackelberg game model. Numerical simulation shows that, compared with the existing spectrum leasing schemes based on cooperative relaying, the proposed scheme can concurrently afford both PN and SN with higher leasing utilities, encourage them to join spectrum leasing, and achieve a better utilization of limited spectrum resources.

To overcome the constraint of spectrum heterogeneity, i.e., different spatial locations may have different available spectrum resources, a cognitive radio ad hoc network (CRAHN) should exchange necessary control information among nodes. To improve the performance of this exchange, the present paper proposes to establish a cluster-based Hamiltonian cycle within the CRAHN to provide an ordered flow of control information among clusters and reduce the collision and delay for control information exchange. Moreover, to offer a better clustering result for this establishment, we also design a novel distributed mechanism for randomly selecting a unique node to collect network information and develop an efficient layered clustering algorithm based on the collected information. Numerical simulation shows that, compared with the existing methods, the proposed collection mechanism is more efficient and incurs less packet collisions in collecting network information, while the proposed clustering algorithm yields a smaller average number of clusters under the condition that each cluster has at least one control channel and helps reducing the overhead of control information exchange.

A ‘fibre‐switch block’ is a switch with delay lines that feedback from some outputs to inputs. In every unit time, it receives and transmits a packet concurrently. A ‘fibre memory’ means a multi‐block serial connection. Its performance of time‐multiplexed operation is often said to ‘emulate’ a multistage interconnection network. This study formulates this concept of emulation. The formalised concept is useful in the design and validation of various switching functionalities, including timeslot interchanging, sorting, merging and concentration. For illustration, ‘banyan‐type networks’, ‘Clos network’ and several familiar multi‐stage sorting networks are all efficiently emulated.

To improve the utilization of spectrum resource, a primary network can share its unused bandwidth with a closely located secondary network. As a compensation, the latter should pay a certain price for the obtained bandwidth. To determine this price under the constraint that the primary network only knows an incomplete information for the utility of the secondary network, the present paper consider the repeated offering of a price from the primary network to the secondary network, which then can accept or reject it, until they reach a price agreement. Since this bargaining process helps the primary network estimate the real utility of the secondary network as accurate as possible, the agreed price is mutually beneficial for both networks. Moreover, to increase the satisfaction of all secondary terminals in transmitting heterogeneous applications, i.e., voice, video, image, and data, we also propose a spectrum allocation solution within the secondary network based on Nash bargaining model. Numerical simulation shows that the benefits of the two networks from spectrum sharing varies with their maximal bargaining times and the proposed spectrum allocation scheme can improve the total satisfaction of all secondary terminals while maintain a reasonable fairness among them.

This paper considers a packet multiplexer (resp. de multiplexer) in the form of a queue with a single time-multiplexed input (resp. output) line, which is called a multiplexing queue (resp. demultiplexing queue). This queue is abstractly formulated in a way that allows recursive construction via 2-stage interconnection. The theoretic underpinning of this recursive construction is the preservation of two types of conditionally nonblocking switches through two versions of the 2-stage interconnection network. The recursive construction of a mux/demux queue emulates such switch preservation into a serial connection of fiber-switch blocks, which combine optical switches with fiber delay lines. Moreover, appropriate tandem connection between these two devices makes a FIFO queue. In terms of the physical structure, an instance of the FIFO queue so constructed coincides with the existing construction in the literature. The switching control mechanisms are different though. Inheriting the unique-routing characteristic of the 2-stage interconnection network, the present construction is under faster control, which distributes the computation task to individual blocks.

A multistage interconnection network (MIN) consisting of 2 times 2 nodes constructs a nonblocking switch if the network is rearrangeable. When a 2ntimes 2nbit-permuting network is rearrangeable with the minimum depth of 2n-1, the initial (resp. final) n stages of the network form a banyan-type network and hence the network is equivalent to the tandem connection between two banyan-type networks. Let gamma denote the guide permutation of a 2ntimes 2nbanyan-type network and tau the trace permutation of another. These are permutations on numbers from 1 to n. This paper proves that, when the permutation gammatau-1is the transposition between the number n and some number k < n, the tandem connection between the two networks is rearrangeable. This sufficient condition for rearrangeability covers a wide class of tandem connections. For example, the first network in tandem can be the omega network appended with the banyan exchange of any rank while the second is the reversed omega network.

The 2-stage interconnection network is the most compact design in recursive construction of switches. Its 2X and X2 versions preserve several types of conditionally nonblocking switches and thereby enable recursive construction. This paper introduces hybrid preservation of new types of conditionally nonblocking switches. One application is in the construction of distributors.

To enhance the access flexibility and logical elasticity in the use as delay lines, fibers are combined with optical switches into various types of fiber memories. One type belongs to recursively constructed packet buffers with single-stream I/O for such applications as queueing, multiplexing, demultiplexing, and flexible delay. The present paper considers the switching control speed over some of such fiber-memory applications.

The two-stage interconnection network is conceivably the most compact design for interconnecting small switches into a large switch. Switches so constructed typically can be controlled in the self-routing manner, because the route from an input to an output is unique. Different orderings of network input/output result in different versions of the two-stage interconnection network, two of which are known to preserve various classes of conditionally nonblocking switches. This paper adds Latin-square switches, rotators, reflectors, twisters, and untwisters to this set of classes with applications in load balancing, crosstalk-free optical switching, full connectivity among multiple users, etc. Knowledge of switch preservation under a certain style of multistage interconnection not only allows recursive construction of indefinitely large switches, but also provides insight, generality, and algorithmic flexibility in the construction

This paper deals with flexibility, rather than efficiency, in information propagation. When optical, electrical, or acoustical signals are guided through their transmission medium, it is possible to store and retrieve their analog form for the purposes of queueing, time slot interchanging, multiplexing, demultiplexing, flexible delay, etc. To harness the constantly progressing signals, the analog memory need be equipped with switches for access flexibility and logical elasticity. This paper proposes systematic algorithms for recursive construction of analog memory via most basic interconnection patterns. The mathematical underpinning is mainly the algebraic theory on 2-stage interconnection networks, over which the switching control is self-routing and fast

The 2-stage interconnection network is conceivably the most compact design for interconnecting small switches into a large switch. When a certain class of switches is preserved under 2-stage interconnection, recursive application of 2-stage interconnection then builds indefinitely large switches in this class from atomic ones. The present paper studies switches that are not preserved under 2-stage interconnection but are yet constructive from atomic elements through recursive 2-stage interconnection. The principle is "mixed preservation" based on the following two properties: first, the 2-stage interconnection network constructs a class-A switch when switches at nodes on one stage belong to class A and switches at nodes on the other stage belong to class B; second, class-B switches are preserved under 2-stage interconnection. A class of conditionally nonblocking switches for such mixed preservation are identified, which are useful in the recursive construction of distribution networks

The most compact pattern for interconnecting small switches into a large switch is conceivably the 2-stage interconnection network. A certain version of a 2-stage interconnection network is said to preserve switches with a certain attribute when the network constructs such a switch from smaller ones at nodes. Recursive application of this version of 2-stage interconnection then leads to the construction of indefinitely large switches with the same attribute. The present paper studies a few new classes of switches that are preserved under 2-stage interconnection and also identifies their applications. Different switch preservation theorems presented in the paper offer the advantages of both the algorithmic flexibility and the theoretic insight.

The cascade of two 2^n × 2^n baseline networks in tandem and the cascade of two omega networks through a special interconnection pattern are known to be rearrangeable. These belong to the general problem: for what two banyan-type networks (i.e., bitpermuting unique-routing network) are their tandem cascade a rearrangeable network? We relate the problem to the trace and guide of banyan-type networks. When the guide of one 2^n × 2^n banyan-type network and the trace of the other are represented by the permutations y and t on integers 1 to n, respectively, rearrangeability of their tandem cascade is solely determined by yt^-1, which is said to be a tandem rearrangeable permutation when the tandem cascade is indeed rearrangeable. We identify a few tandem rearrangeable permutations, each implying the rearrangeability of the tandem cascade of a wide class of banyan-type networks.