Exploiting Cooperative Advantages in Slotted ALOHA Random Access Networks

In this work, we study the finite-user stability region of a slotted ALOHA random access network with cooperative users. The network consists of multiple cooperating pairs where the users in each pair is allowed to cooperate by relaying each others' messages to the access point (AP). Spatial diversity gains are achieved since the packet of a cooperative user can be transmitted through independent fading channels, eg. the direct transmission path and the cooperative relaying path. Most works in the literature on cooperative communications focus on the physical layer aspects such as coding, modulation, transceiver signal processing etc. In this paper, we study the advantages of user cooperation from a MAC layer perspective and devise queueing strategies to exploit the cooperative diversity gains in a random access network. Extending upon our previous results for the two-user case, we study the stability of the finite-user cooperative system that consists of multiple cooperating pairs. By treating each cooperative pair as a transmission entity, we derive inner bounds for the finite-user stability region and propose a ranking system to characterize the transmission entities' relative tendency of being stable (or unstable).

In this letter, a new secure information transmission scheme based on polar codes with a pre-shared secret key is proposed. In polar codes, after the channel polarization is induced, good split channels are used to transmit the user message and bad channels are utilized to support the reconstruction of the message by sharing fixed information. If the fixed information in bad channels is secret, an adversary gets difficulty in reconstructing the user message in good channels without knowledge of the fixed information. From this observation, we construct a secure information transmission scheme. By appending pre-/post-processing that imposes a dependency between the transmitted message sub-blocks, the adversary's difficulty can be changed to an intractability, since only partial information can be decodable by attackers. A new class of secret key scheme is developed in such a way.

Multi-rate capabilities are supported by the physical layers of most 802.11 devices. To enhance the network throughput of MANETs, transfer rate adaptation at MAC layer should employ the multi-rate capability at physical and the information of previous transmissions provided by MAC and physical layers. In this paper, we propose a transfer rate adaptation scheme plus back-to-back frame transmissions, and fragmentation at MAC layer, named TRAF. TRAF adopts a bi-direction-based approach with an extended option to select an appropriate rate for frame transmission under fast changing channel conditions. Consecutive back-to-back frame transmissions to fully utilize good channel quality during a coherent time interval and fragmentation algorithm to maintain high throughput under worse channel conditions are recommended in TRAF. Extensive simulation is experimented to evaluate the performance of TRAF. Regarding simulation results, frame delivery ratio, and network throughput of TRAF are significantly improved by comparing to that of other protocols.

Focusing on the low throughput of fair subcarrier allocation in cooperative OFDMA system, an improved algorithm with single subcarrier capacity threshold and cooperative power factor is proposed. In this algorithm, the users with bad channel can not occupy too many subcarrier, and the power for cooperating with other users of users with good channel is limited. Simulation results show that this algorithm can increase the total channel capacity with less loss of fairness.

Although cooperative communication has been proposed at the physical layer to address multi-path fading effects, how physical layer gains with cooperative communication can translate to tangible performance benefits in end-to-end flows remains to be an open problem. This paper represents one step forward towards a deeper understanding of the interplay between end-to-end throughput and physical layer cooperative communication, in the general context of multi-hop multi-channel wireless networks. Based on a decode-and-forward physical layer design with rateless codes, we reformulate the problem of routing and channel assignment to account for physical layer cooperation. We design a distributed protocol to solve the new problem. Our simulation results have validated the effectiveness of our protocol to offer a substantial gain with respect to stabilizing the offered aggregate throughput in the network.Keywordscooperative communicationchannel assignmentmulti-hop multi-channel wireless networks

For satellite systems offering broadband and telecom services at Ka band frequencies and above Fade Mitigation Techniques (FMT), in particular Adaptive Modulation and Coding (ACM), are essential to improve the system capacity. One of the important aspects of ACM from a physical and MAC layer perspective is the choice of transmission modes to be used during the system operation that would achieve the optimal trade-off between the system complexity and performance. This paper deals with one such methodology of selecting the appropriate set of transmission modes (MODCOD subset) from a physical layer point of view for both DVB-S2 and extended DVB-RCS systems. Optimizing the achievable spectral efficiency with respect to implementation complexity has been the main focus of the proposed methodology. In particular, we show that subsets with 8 and 5 transmission modes provide best trade-off between the complexity of the ACM based system and the achieved average spectral efficiency for the forward and return link of the DVB-S2/RCS system respectively.

This paper addresses the medium access control (MAC) and physical (PHY) cross-layer design of a time-division multiple access protocol (TDMA) where users with good channels are allowed to relay the packets of other users with less favorable conditions. All signals are combined at the central node using signal processing tools in order to achieve diversity. The work is focused on an asymmetrical scenario where users experience different channel and queuing states. Two performance metrics are used: packet throughput and access delay. To facilitate the analysis, a packet reception model which represents more efficiently the cooperative PHY layer is also proposed. A multi-objective optimization is used to derive the boundaries of the throughput region, i.e., the set of all achievable user throughput values. Sketches of the two-user case show that the region is always convex and larger than the region of its non-cooperative counterpart. The results also show that cooperation is useful when some users with good channels experience low/medium traffic loads and thus can help other users with bad channels and higher traffic loads. Evaluation of access delay is also obtained by using the expressions of a modified TDMA system.

In this paper, we investigate some cross-layer cooperative strategies for cognitive Time-Division Multiple-Access relay channels with bursty arrivals. The proposed schemes adopt an advanced physical (PHY) layer cooperation and an “intelligent” cognitive network-layer cooperation in order to improve the stable throughput region of the system. In contrast to previously reported work, where relaying is only enabled on periods of source silence, here, we incorporate a Dynamic Decode-and-Forward (DDF) policy which allows relaying assistance also during the source transmission. The enhancement of cognitive relaying with DDF provides more cooperative opportunities which results in faster emptying of the user queues and higher stable throughput compared to the conventional approaches. In addition to this PHY-layer relaying, the cognitive cooperation is supported by an adaptive/non-adaptive superposition scheme which allows the relay node to simultaneously forward packets from different users. We demonstrate that superposition can further increase the transmission opportunities and significantly improve the stable throughput region. The proposed schemes are studied from a networking perspective and their advantages are shown through both theoretical results and computer simulations.

In this paper, we develop a physical/medium-access-control (PHY/MAC) cross-layer analytical model to investigate the throughput performance of the wireless local-area network (WLAN) in a lossy wireless environment. From the PHY-layer perspective, the developed model incorporates the effects of capture and directional antennas, while from the MAC-layer perspective, our approach takes into account the carrier-sense multiple access with collision-avoidance (CSMA/CA) MAC protocol and the effect of the backoff process in the IEEE 802.11 WLAN. We derive explicit analytical expressions for the frame outage and capture probabilities of a directional antenna system in the presence of shadowing and Rayleigh fading. Applying this analysis, we can model the interaction between the PHY and MAC layers more accurately for the infrastructure-based WLAN. The numerical results show that our analytical model can approach that attained by simulations. The proposed cross-layer analytical model not only provides insights into the PHY layer impacts on the throughput of the CSMA/CA MAC protocol but also indicates to how directional antennas can improve the CSMA/CA-based WLAN in terms of antenna beamwidth and the number of radio transceivers.

On the impact of the physical layer model on the performance of D2D-offloading in vehicular environments

Applying multimedia to Wireless Sensor Network (WSN) adds more challenges due to WSN resource constraints and the strict Quality of Service (QoS) requirements for multimedia transmission. Different multimedia applications may have different QoS requirements, so routing protocols designed for Wireless Multimedia Sensor Network (WMSN) should be conversant of these requirements and challenges in order to ensure the efficient use of resources to transfer multimedia packets in an utmost manner. The majority of solutions proposed for WMSN depends on traditional layered based mechanisms which are inefficient for multimedia transmission. In this paper we propose a cross-layer Ant based Routing Protocol for WMSN (CARPM) by using modified ant colony optimization (ACO) technique to enhance the routing efficiency. The proposed protocol uses an improved ACO to search for the best path that are satisfied with the multimedia traffic requirements. While making best decision the weightage is given to energy consumption, and queuing delay. The proposed cross layer scheme works between the routing, MAC, and physical layers. Since, the remaining power and timestamp metrics are exchanged from physical layer to network layer. Dynamics duty cycle assignment is proposed at MAC layer which changes according to traffic rate. The presented algorithm is simulated using NS2 and is proven to satisfy its goals through a series of simulations.

Channel quality has a great influence on bit error rate (BER) of received signal. The scheme to efficiently ensure four kinds of data services provided by IEEE 802.16 standards is an interesting research issue. In this paper, we propose an adaptive scheduling algorithm cross physical (PHY) layer and MAC layer for IEEE 802.16 BWA system. The Signal to Noise Ratio (SNR) on wireless fading channels determines the modulation and coding (AMC) scheme and the quantity of transmitted packets at the PHY layer. The objective of the AMC coding scheme is maximize packets throughput while maintaining the BER requirement. At the MAC layer, the algorithm scheduling the packets to ensure diverse QoS requirements for multiple connections, e.g., delay for rtPS, throughput for nrtPS, and fairness for BE. To obtain optimal scheduling, we define the cost function for each connection based on channel condition, service status, throughput or deadline. We also verify the analytic results using computer simulation. The simulation results show that our proposed scheduler can provide diverse QoS guarantees, maximum throughput and achieve an optimal tradeoff between throughput and fairness.

In this paper, we propose a novel adaptive carrier sense multiple access scheme with collision avoidance (CSMA/CA) to perform efficient and reliable data transfer with increased throughput across multiple coexisting wireless body area networks (BANs) in a tiered architecture. We investigate the proposed scheme using two distributed cross-layer optimized dynamic routing techniques, i.e., shortest path routing (SPR) and cooperative multi-path routing (CMR). The channel state information from the physical layer is passed on to the network layer using an adaptive cross-layer carrier sensing mechanism between the physical and MAC layer, which adjusts the carrier sense threshold (e.g., RSSI) periodically based on the slowly-varying channel condition. An open-access experimental dataset of 'everyday' mixed-activities is used for analyzing the cross-layer optimization. Our proposed optimization using adaptive carrier sensing performs better than static carrier sensing with CSMA/CA as it reduces the continuous back-off duration and latency as well as significantly increases the throughput (in successful packets/s) by more than 50%. Adaptive CSMA/CA also shows 20% and 6% improvement over a coordinated TDMA approach with higher duty cycle for throughput and spectral efficiency, respectively, and provides acceptable packet delivery ratio and outage probability with respect to SINR.

The Cellular Digital Packet Data (CDPD) system is the first public wireless data ever deployed in the US. As its traffic continues to grow, potential new customers require to know the platform's quality-of-service (QoS) performance data prior to subscribing to the service. Consequently, network planners are searching for a simple model which can provide QoS analysis instantly, rather than conducting long (and costly) simulations. This paper provides such model. CDPD uses a random-access MAC layer protocol known as the DSMA/CD, to control the users packet transmission on the reverse link. In general, the success of the transmitted packets, as well as the delay incurred, depends heavily on both: the efficiency with which the DSMA/CD controls packet collisions, and the degree of error-free reception provided by the physical layer. Therefore, one must consider the joint operation of the two in order to produce quotable realistic traffic performance figures. This paper focuses on the joint operation of the two named layers.

Consider a time slotted multiuser random access network where M users have access to a single channel and each user attempts to send packets in a particular time slot with a certain probability, according to a predetermined access scheme. This forms an interacting system of queues and in this study, the authors consider generic access schemes that satisfy a separability condition and obtain bounds for the stability region, directly using a Lyapunov-type analysis. They apply their results to the case of random access networks with partial conflicts where any particular user has collision conflicts with only a subset of the other users. Using conflict graphs to quantify the degree of such conflicts, they obtain bounds for the stability region for both deterministic and random conflict graphs that model, respectively, static and mobile networks.