167 research outputs found
Medium access control design for all-IP and ad hoc wireless network
Medium Access Control (MAC) protocol in a wireless network controls the access of wireless medium by mobile terminals, in order to achieve its fair and efficient sharing. It plays an important role in resource management and QoS support for applications. All-IP wireless WAN is fully IP protocol-based and it is a strong candidate beyond 3G (Third Generation Wireless Network). Ad hoc wireless network has recently been the topic of extensive research due to its ability to work properly without fixed infrastructure.
This dissertation is composed of two main parts. The first part pursues a Prioritized Parallel Transmission MAC (PPTM) design for All-IP Wireless WAN. Two stages are used and each packet is with a priority level in PPTM. In stage 1, a pretransmission probability is calculated according to the continuous observation of the channel load for a certain period of time. In stage 2, a packet is prioritized and transmitted accordingly. It is modeled and analyzed as a nonpreemptive Head-Of-the-Line prioritized queueing system with Poisson arrival traffic pattern. Its performance is analyzed under three other traffic patterns, which are Constant Bit Rate, Exponential On/Off, and Pareto On/Off, by using a NS-2 simulator, and compared with that of Modified Channel Load Sensing Protocol. PPTM supports dynamic spread code allocation mechanism. A mobile terminal can apply for a spreading code according to the current channel condition.
To use the idea of dynamic bandwidth allocation in PPTM for adhoc wireless network, a Dynamic-Rate-with-Collision-Avoidance (DRCA) MAC protocol is proposed in the second part of the dissertation. DRCA is based on spread spectrum technology. In DRCA, a terminal sets the spreading factor for a packet according to the activity level of neighboring nodes. If the total number of usable spreading codes with this spreading factor is less than the total number of mobile terminals in the network, to avoid collision, the spreading code id is broadcast such that other terminals can avoid using it when the packet is being transmitted. The performance of DRCA is theoretically analyzed in a slotted, single-hop, multi-user environment. To evaluate DRCA\u27s performance in an environment closed to a real one, a simulator that supports multi-hop, random mobility pattern is created with OPNET. Both theoretical and simulation results show that DRCA outperforms MACA/CT (Multiple Access with Collision Avoidance with Common Transmitter-based) in case if there are more than one communication pair and the ratio of inactive mobile terminals to active ones is high
Analysis and evaluation of decentralized multiaccess Mac for ad-hoc networks
In mobile ad-hoc radio networks, terminals are mobile and
heterogeneous, the architecture of the network is continuously
changing, communication links are packet oriented and radio
resources are scarce. Therefore, mechanisms on how to access
the radio channel are extremely important in order to improve
network efficiency and, when needed, to guarantee QoS.
However, due to these network harsh conditions, decentralized
Medium Access Control (MAC) protocols designed
specifically for ad hoc networks are scarce. In this paper we
present a novel decentralized multiaccess MAC protocol for
Ad Hoc networks. This MAC protocol is an hybrid CDMATDMA
in which a cross layer approach has been followed in
order to maximize network throughput. A theoretical analysis
of the system is presented ending up with closed expressions
for the throughput and delay of the network and some
simulations are presented to evaluate the performance of the
system.Postprint (published version
Decentralised multi-access MAC protocol for ad-hoc networks
In ad-hoc radio networks, mechanisms on how to access the radio channel are extremely important in order to improve network efficiency and, when needed, to guarantee QoS.
Traditionally, Medium Access Control (MAC) protocols in ad hoc networks have been designed to face off the well known
collision resolution problem. However, when using advanced signal processing techniques, general assumptions on collisions and
packet loss are no longer valid. Besides, little has been reported about MAC algorithms dealing with multiaccess channels in ad hoc networks. In this paper, we present a novel decentralized multiaccess MAC protocol for Ad Hoc networks. This MAC
protocol is an hybrid CDMA-TDMA in which a cross layer approach has been followed to dinamically adapt to the traffic load. Closed expressions for the throughput and delay of the network are presented as a function of the multipacket reception
capability of the receiver, the number of codes and the packet retransmission probability.Postprint (published version
Medium access control with physical-layer-assisted link differentiation
In this paper, we develop medium access control (MAC) schemes for both contention and contention-free accesses over wireless local area networks and give performance analysis of these MAC protocols. User detection and multirate adaptation (MRA) modules are proposed in the physical layer (PHY) to assist link differentiation. With these two modules, for contention accesses, a new distributed queuing MAC protocol (PALD-DQMP) is proposed. Based on different users' channel states, PALD-DQMP makes use of a distributed queuing system to schedule transmissions. To support multimedia transmissions, an enhanced PALD-DQMP (E-PALD-DQMP) is designed by providing two-level optimized transmission scheduling for four access categories, thus eliminating both external and internal collisions among mobile stations. For contention-free accesses, based on the same PHY-assisted link differentiation provided by the two modules, a new multipolling MAC protocol (PALD-MPMP) is proposed, which not only reduces the polling overhead but also prioritizes transmissions according to their delay requirements. Performance analysis and simulation results show that our proposed protocols outperform the standard MAC protocols for both delay-sensitive and best-effort traffics. All these improvements are mainly attributed to the awareness of cross-layer channel state information and the consequent MRA scheme. © 2008 IEEE.published_or_final_versio
A distributed wireless MAC scheme for service differentiation in WLANs.
Mobile communications is evolving due to the recent technological achievements in wireless networking. Today, wireless networks exist in many forms, providing different types of services in a range of local, wide area and global coverage. The most widely used WLAN standard today is IEEE 802.11. However, it still has problems with providing the QoS required for multimedia services using distributed methods. In this thesis, a new distributed MAC scheme is proposed to support QoS in wireless LANs. In the scheme, stations use CSMA for channel access, with collisions between stations being resolved by sending a set of beacons in a predefined manner, and virtual collisions being resolved by schedulers at the stations. The proposed MAC scheme is analyzed mathematically, for two-priority case, and the results obtained are validated by simulation. The mathematical model estimates the average delay experienced by data packets of priority one and two under different conditions. A performance evaluation study of the proposed MAC scheme as well as the IEEE 802.11 DCF, and IEEE 802.11e EDCF MAC schemes is also done by means of stochastic simulation. It is found that the results obtained by simulation are in very good agreement with the analytical results, thereby validating them. Moreover, the simulation study evaluated different performance measures of these MAC schemes. The results showed that the IEEE 802.11 DCF scheme does not support QoS, but the proposed MAC scheme and the upcoming IEEE 802.11 EDCF both do. In general, the results show that the proposed MAC scheme performs equally or better than the current IEEE 802.11 DCF scheme in every case considered. It is also found that the proposed MAC scheme performs equally well as the upcoming IEEE 802.11e EDCF scheme, in every case considered in this thesis
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
Multi-hop relaying networks in TDD-CDMA systems
The communications phenomena at the end of the 20th century were the Internet and mobile
telephony. Now, entering the new millennium, an effective combination of the two should
become a similarly everyday experience. Current limitations include scarce, exorbitantly priced
bandwidth and considerable power consumption at higher data rates.
Relaying systems use several shorter communications links instead of the conventional
point-to-point transmission. This can allow for a lower power requirement and, due to the
shorter broadcast range, bandwidth re-use may be more efficiently exploited. Code division
multiple access (CDMA) is emerging as one of the most common methods for multi user
access. Combining CDMA with time division duplexing (TDD) provides a system that
supports asymmetric communications and relaying cost-effectively. The capacity of CDMA
may be reduced by interference from other users, hence it is important that the routing of
relays is performed to minimise interference at receivers.
This thesis analyses relaying within the context of TDD-CDMA systems. Such a system was
included in the initial draft of the European 3G specifications as opportunity driven multiple
access (ODMA). Results are presented which demonstrate that ODMA allows for a more
flexible capacity coverage trade-off than non-relaying systems. An investigation into the
interference characteristics of ODMA shows that most interference occurs close to the base
station (BS). Hence it is possible that in-cell routing to avoid the BS may increase capacity.
As a result, a novel hybrid network topology is presented. ODMA uses path loss as a metric
for routing. This technique does not avoid interference, and hence ODMA shows no capacity
increase with the hybrid network. Consequently, a novel interference based routing algorithm
and admission control are developed. When at least half the network is engaged in in-cell
transmission, the interference based system allows for a higher capacity than a conventional
cellular system. In an attempt to reduce transmitted power, a novel congestion based routing algorithm is introduced. This system is shown to have lower power requirement than any other analysed system and, when more than 2 hops are allowed, the highest capacity.
The allocation of time slots affects system performance through co-channel interference. To
attempt to minimise this, a novel dynamic channel allocation (DCA) algorithm is developed
based on the congestion routing algorithm. By combining the global minimisation of system
congestion in both time slots and routing, the DCA further increases throughput. Implementing
congestion routed relaying, especially with DCA, in any TDD-CDMA system with in-cell calls
can show significant performance improvements over conventional cellular systems
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