Analytical BER Performance of DS-CDMA Ad Hoc Networks using Large Area Synchronized Spreading Codes

The family of operational CDMA systems is interference-limited owing to the Inter Symbol Interference (ISI) and the Multiple Access Interference (MAI) encountered. They are interference-limited, because the orthogonality of the spreading codes is typically destroyed by the frequency-selective fading channel and hence complex multiuser detectors have to be used for mitigating these impairments. By contrast, the family of Large Area Synchronous (LAS) codes exhibits an Interference Free Window (IFW), which renders them attractive for employment in cost-efficient quasi-synchronous ad hoc networks dispensing with power control. In this contribution we investigate the performance of LAS DS-CDMA assisted ad hoc networks in the context of a simple infinite mesh of rectilinear node topology and benchmark it against classic DS-CDMA using both random spreading sequences as well as Walsh-Hadamard and Orthogonal Gold codes. It is demonstrated that LAS DS-CDMA exhibits a significantly better performance than the family of classic DS-CDMA systems operating in a quasi-synchronous scenario associated with a high node density, a low number of resolvable paths and a sufficiently high number of RAKE receiver branches

Cross layer optimization in 4G Wireless mesh networks

Wireless networks have been rapidly evolving over the past two decades. It is foreseen that Fourth generation (4G) wireless systems will involve the integration of wireless mesh networks and the 3G wireless systems such as WCDMA. Moreover their wireless mesh routers will provide service to wireless local networks (WLANs) and possibly incorporate MIMO system and smart admission control policies among others. This integration will not only help the service providers cost effectiveness and users connectivities but will also improve and guarantee the QoS criteria. On the other hand, cross layer design has emerged as a new and major thrust in improving the quality of service (QoS) of wireless networks. Cross layer design involves the interaction of various layers of the network hierarchy which could further improve the QoS of the 4G integrated networks. In this work we seek new techniques for improving the overall QoS of integrated 4G systems. Towards this objective we start with the local low tier WLAN access. We then investigate CDMA alternatives to the TDMA access for wireless mesh networks. Cross layer design in wireless mesh networks is then pursued. In the first phase of this thesis a new access mechanism for WLANs is developed, in which users use an optimum transmission probability obtained by estimating the number of stations from the traffic conditions in a sliding window fashion, thereby increasing the throughput compared to the standard DCF and RTS/CTS mechanism while maintaining the same fairness and the delay performance. In the second phase we introduce a code division multiple access/Time division duplex technique CDMA/TDD for wireless mesh networks, we outline the transmitter and receiver for the relay nodes and evaluate the efficiency, delay and delay jitter performances. This CDMA based technique is more amenable to integrating the two systems (Mesh networks and WCDMA or CDMA 2000 of3G). We compare these results with the TDMA operation and through analysis we prove that the CDMA system outperforms the TDMA counterparts. In the third phase we proceed to an instance of cross layer optimized networks, where we develop an overall optimization routine that finds simultaneously the best route and the best capacity allocation to various nodes. This optimization routine minimizes the average end to end packet delay over all calls subject to various contraints. In the process we use a new adaptive version of Spatial TDMA as a platform for comparison purposes of the MAC techniques involved in the cross layer design. In this phase we also combine CDMA/TDD and optimum routing for cross layer design in wireless mesh networks. We compare the results of the CDMA/TDD system with results obtained from the STDMA system. In our analysis we consider the parallel transmissions of mesh nodes in a mesh topology. These parallel transmissions will increase the capacity resulting in a higher throughput with a lower delay. This will allow the service providers to accommodate more users in their system which will obviously reduce the colt and the end users will enjoy a better service paying a lower amount

Analytical Bit Error Rate Performance of DS-CDMA Ad Hoc Networks using Large Area Synchronous Spreading Sequences

The performance of large area synchronous (LAS) direct sequence code division multiple access (DS-CDMA) assisted ad hoc networks is investigated in the context of a single-hop infinite mesh of rectilinearly located ad hoc nodes. It is shown that LAS DS-CDMA exhibits a significantly better performance than the family of traditional spreading sequences used in a quasisynchronous DS-CDMA scenario having a low number of resolvable multipath components and a sufficiently high number of RAKE receiver branches. The benefits of LAS codes in ad hoc networks are multifold: (i) Their performance is noise-limited, rather than interference-limited, provided that the multipath and multi-user interference arrives within their interference free window. (ii) Under the same conditions LAS codes are robust against the ‘near–far’ effects imposed by ad hoc networks operating without base-station-aided power control, without accurate synchronisation and without implementationally complex interference cancellers

Voice Service Support in Mobile Ad Hoc Networks

Mobile ad hoc networks are expected to support voice traffic. The requirement for small delay and jitter of voice traffic poses a significant challenge for medium access control (MAC) in such networks. User mobility makes it more complex due to the associated dynamic path attenuation. In this paper, a MAC scheme for mobile ad hoc networks supporting voice traffic is proposed. With the aid of a low-power probe prior to DATA transmissions, resource reservation is achieved in a distributed manner, thus leading to small delay and jitter. The proposed scheme can automatically adapt to dynamic path attenuation in a mobile environment. Simulation results demonstrate the effectiveness of the proposed scheme.Comment: To appear in the Proceedings of the IEEE Global Communications Conference (GLOBECOM), Washington, DC, November 26 - 30, 200

An Energy-Efficient Reconfigurable Circuit Switched Network-on-Chip

Network-on-Chip (NoC) is an energy-efficient on-chip communication architecture for multi-tile System-on-Chip (SoC) architectures. The SoC architecture, including its run-time software, can replace inflexible ASICs for future ambient systems. These ambient systems have to be flexible as well as energy-efficient. To find an energy-efficient solution for the communication network we analyze three wireless applications. Based on their communication requirements we observe that revisiting of the circuit switching techniques is beneficial. In this paper we propose a new energy-efficient reconfigurable circuit-switched Network-on-Chip. By physically separating the concurrent data streams we reduce the overall energy consumption. The circuit-switched router has been synthesized and analyzed for its power consumption in 0.13 ¿m technology. A 5-port circuit-switched router has an area of 0.05 mm2 and runs at 1075 MHz. The proposed architecture consumes 3.5 times less energy compared to its packet-switched equivalen