In this paper we outline a vision for the Connected Car which is centred around the user's mobile device. We describe the different components of the Connected Car ecosystem and highlight why it will remain very heterogeneous for some time. We describe particular technologies in this space which have real potential to be key technologies in the Connected Car. Finally, we review online services which are relevant for automotive services.

This paper presents the high level specification of a Self Configuration Framework for 802.11 multi-radio Wireless Mesh Networks based on a centralised topology discovery and channel assignment mechanism. The framework was designed to support the introduction of a new Mesh Node into the network at any time of the network's operational phase. Further, it enables a new Mesh Node to locate and communicate with the Mesh Gateway and vice versa before any routing protocol has been activated. Finally, the paper presents an estimation of time required to boot a single node and the entire multi-radio Wireless Mesh Network.

The existence of hidden and exposed nodes can have a significant negative impact on the performance of IEEE802.11 networks. Such nodes can increase the probability of collisions and limit the spatial reuse on the channel. The value of the Physical Carrier Sensing Threshold (PCST) is instrumental in the presence of such nodes in a system. This paper presents a new adaptive physical carrier sensing management algorithm for wireless networks. Our KAPCS2 management system maximizes the aggregate system throughput by identifying and addressing problem nodes. It incorporates 802.11k Radio Resource Measurements (RRM) on each node to enable on-line tuning of the PCST.

The availability of reasonably priced, increasingly powerful, mobile devices is driving the growth of new video content services. One likely solution for video content delivery is based on the Peer-to-Peer (P2P) architecture. Network congestion can have a significantly negative impact on the performance of P2P distribution. This paper focuses on enabling effective P2P content distribution over radio access networks. We developed a IEEE802.11k assisted mechanism to perform load balancing of peer associations across available networks. Load balancing can reduce congestion and increase throughput. Simulation results show significant throughput increase following a handover.

This paper examines two specific aspects of resource management in Wireless Local Area Networks (WLANs)-Call Admission Control (CAC) and handling of Link Adaptation (LA) events. A self-consistent system to manage these for Voice over Internet Protocol (VoIP) over an IEEE 802.11 WLAN is presented. The proposed CAC scheme is based on the Endpoint Admission Control (EAC) paradigm, where the endpoints probe the network to determine if the call can be supported with acceptable Quality of Service (QoS). The proposed scheme was evaluated on an experimental testbed and test results show that correct admission decisions were made under various network configurations. The scheme also determines if LA has resulted in the system becoming congested and, if so, the voice codec of the handset which has undergone LA is adapted so as to restore the system to its earlier state, thereby alleviating the congestion. The proposed scheme was evaluated on the experimental testbed and test results show that the codec adaptation scheme was very effective at overcoming the effects of LA for VoIP over WLAN.

In this paper, two formulations for planning base station (BS) and Relay Station (RS) locations are proposed: a rather complex 0-1 integer programming model which can be used to determine which set of locations should be selected from a given set of BS and RS locations and a simpler decomposition approach which focuses first on the BS location problem followed by the RS location determination. The two approaches are compared and the results show that the simpler decomposition approach can find solutions using significantly less resources which are very minimally lower in quality than that found by the more complex formulation. Hence, the decomposition approach can be used to solve larger 802.16j network planning problems.

In this paper, the system capacity of a multi-cell IEEE 802.16j system operating in transparent mode is investigated. A previous published analytical model is used and incorporates interference from neighbouring cells. The model can be used to determine downlink performance under max-min fairness constraints for both sectored and omnidirectional systems with different amounts of relays. The study provides guidelines on the design of 802.16j systems operating in transparent mode specifically, how to maximise throughput for such systems. It is shown that inter-cell interference from relays is limited in a suburban environment and that relays can deliver significant gains over single hop systems: gains of 30% and 60% can be achieved without and with spatial reuse in an omnidirectional system while 15% and 25% in a sectorised system.

Wireless mesh networking is a promising, cost effective and efficient technology for realizing backhaul networks supporting high quality services. In such networks, multicast data are transmitted blindly without any mechanism protecting data from loss, ensuring data reception, and optimizing channel allocation. The multicast services may undergo, then, very high data loss ratio which is exacerbated with the number of hops. In this paper, we propose a Reliable Multicast Distribution System (RMDS) to optimize multicast packets transmission in bridged networks. Relying on a modification of the IGMP snooping protocol, RMDS enables reliable services provisioning support in common wireless mesh networks. In particular, RMDS only exploits the local knowledge of a particular node to compute the multicast tree, which significantly reduces the signalling overhead in comparison with network layer and overlay solutions. Simulation results elucidate that RMDS optimizes resources' allocation by reducing significantly the network load, the media access delay and the data drop rate compared to the classical approach, which is based on the combination of spanning tree algorithm and IGMP snooping protocol.

In this paper, the system capacity of IEEE 802.16j systems operating in transparent mode is investigated under varying numbers of relays and associated transmit power. The study is based on an extended variant of an analytical model defined in previous work and used to determine the throughput gain that can be achieved under a max-min fairness constraint. The study finds that significant overall throughput gains can be achieved over 802.16e systems: 125% and 55% gain with and without spatial reuse, respectively. However, the overall throughput gain drops as the transmit power at the relays (RSs) decreases despite the fact that a greater number of concurrent transmissions can be achieved due to less interference among the RSs' transmissions. Decreasing the transmit power at the RSs eventually leads to a significant reduction of the achievable throughput gain even though a large number of RSs are deployed in scenarios with or without spatial reuse.

In this paper, a problem formulation for determining optimal node location for base stations (BSs) and relay stations (RSs) in relay-based 802.16 networks is developed. The formulation results in an Integer Programming problem. A small modification to the original model is also considered in which the state space is reduced by limiting which nodes can be associated with which. Standard branch and bound techniques are used to solve the problem. The key findings of the paper are that standard techniques can be used to find solutions to problems of small metropolitan scale or for areas within a larger city.

In this paper, a clustering approach to solve a network planning problem for 802.16J relay networks is considered. Our clustering approach consists of three basic steps: (1) divide the nodes into k distinct clusters, (2) solve the planning problem separately for each cluster, and (3) perform a final optimization to reduce issues arising at cluster boundaries. Simulation results show that our approach is more efficient than existing approaches: solutions of equivalent quality can be found in 40% of the time. Thus our technique can be used to solve larger problems with similar hardware, or similar size problems in less time.

Current Internet use is evolving, users are becoming mobile and are expecting data services on the go. This fact presents big challenges and opportunities to operators, which see the increase in data services as a big market still to be exploited. However, current cellular technologies cannot accommodate the demand that will arise when the true Mobile Internet evolves. Addressing these challenges, we present the CARMEN project, the vision of which is to extend operators’ infrastructure by providing carrier grade services through a heterogeneous wireless mesh. The CARMEN architecture will provide enough bandwidth to cope with users’ expectations at a reduced cost, thereby generating major benefits to operators and users.

Existing terminal oriented handover mechanisms capable of meeting the strict delay bounds of real time applications such as VoIP do not consider the QoS of candidate handover networks. In this paper ECHO - a QoS based handover solution for VoIP- is proposed. ECHO is endpoint centric and does not require any network support; it leverages the SCTP transport protocol. ECHO incorporates network metrics that directly affect VoIP quality into the handover decision process. A dynamic variant of the ITU-T E-Model is used to calculate how the network metrics map to a user perceived voice quality metric known as the MOS. The MOS value is then used to make handover decisions between each of the available access networks. The results show that the addition of the QoS capabilities significantly improves the handover decisions that are made.

An approach to mitigating interference between 802.16 license-exempt systems is proposed in this paper. More specifically, the approach focuses on solving problems which arise when two or more 802.16 systems operate on the same channel in close proximity to each other. The essence of the approach is a distributed mechanism which can apportion the available OFDM subcarriers between the different 802.16 systems. Simulation results show that the topology and the distributions of base stations (BSs) and the subscriber stations (SSs) have a significant impact on the system performance. Also, the system is very sensitive to the order in which the different nodes in the system are activated. Furthermore, the system with the given parameters can operate satisfactorily for up to 6 BSs in the same area, but scalability problems arise if more BSs are added.

In this paper a transport layer handover mechanism for Voice over Internet Protocol (VoIP) using the Stream Control Transmission Protocol (SCTP) is proposed. This handover mechanism utilizes the multi-homing feature of SCTP to allow connection to multiple wireless networks. Each available wireless network is probed with simulated VoIP data to obtain network performance metrics. Handover decisions are made based on the Mean Opinion Score (MOS) calculated from the ITU-T E-Model for voice quality assessment using the obtained measurements. Implementation and simulations were carried out using the NS2 network simulator. The results show the MOS obtained using the proposed handover mechanism on IEEE 802.11b WLAN access points (APs) under varying load conditions. High correlation is shown between the MOS from the proposed handover scheme and the MOS experienced by a VoIP node present in the network. A simulation showing an SCTP endpoint handover between AP's is presented.

In this paper a scheme is proposed to deal with congestion problems that can arise due to Link Adaptation (LA) in Wireless Local Area Networks (WLANs) in the presence of VoIP traffic. The proposed scheme operates by first determining if LA has resulted in the system becoming congested. If not, no further action is taken. However, if, LA has resulted in an overloaded system, the voice codec of the handset which has undergone LA is adapted so as to restore the system to its earlier state, thereby alleviating the congestion. This is achieved by specifically adapting the codec so as to maintain approximately the same level of medium usage as was used prior to the LA. The proposed scheme was evaluated on an experimental test-bed and results show that the codec adaptation was very effective at overcoming the problem of LA.

In this paper a transport layer handover mechanism for Voice over Internet Protocol (VoIP) in 802.11b using the Stream Control Transmission Protocol (SCTP) is proposed. The multi-homing feature of SCTP is used to allow connections to several 802.11b Access Points (AP's). Probing packets that model VoIP encoded data at various transmission rates are used to obtain quality metrics from each of the available networks. Handover decisions are made based on the Mean Opinion Score (MOS) calculated from the ITU-T E-Model for voice quality assessment using the obtained measurements. The handover mechanism is shown to operate in 802.11b networks with heterogeneous transmission rates using multiple VoIP codecs. The results show a high correlation between the MOS predicted by the proposed mechanism and the MOS experienced by a VoIP call present in the network. Results verify the accurate operation of the scheme using multiple VoIP codecs at various transmission rates. A simulation showing an SCTP endpoint handover between heterogeneous transmission rate AP's is presented.

Abstract — This paper presents how SCTP can stall in multihomed scenarios during failover and under certain circumstances. A stall is where an SCTP end-point ceases to communicate for an extended period of time, but does not report any error to the upper layer. This paper presents two different sets of circumstances where a stall can occur: firstly when there is an underestimation of the Retransmission Time-Out (RTO) value for a redundant network path; and secondly when a network error occurs that causes only SACKs to be lost, which confuses the SCTP sender about which network path is operational. Solutions to both of these stalls are presented that include modifying the RTO value, applying Karn’s algorithm to path monitoring and ensuring the destination address selection policy for SACKs is changed. This paper also presents a mechanism to de-couple data acknowledgement and path monitoring when using multi-homed transport protocols, which should remove the ambiguity about path monitoring and offers a universal solution to the stall. I.

The seamless handover of streamed video in a WLAN with UDP as the transport layer is considered. The use of handover for stationary nodes in the case of network congestion is motivated. Next, the relationship between delay and loss in WLANs is studied, with the conclusion that delay can be used as an indicator of when loss is likely to occur. Delay can therefore be used as a basis of a handover scheme which can minimize loss. Such a handover scheme is proposed in which the client makes two simultaneous connections to the same server through two separate WLANs, and it is shown that the client can use the relative packet delay between the two streams to determine which network delivers the best performance; this information is then used to determine when to perform a handover. The proposed scheme is implemented and results are presented that show the successful handover of an RTP over UDP stream using this scheme in a live WLAN environment.

A study of the performance of a number of different multiplexing schemes was conducted in the context of streaming of MPEG-4 object-based content, with particular emphasis on streaming content to mobile devices. The comparison involved six different schemes. The schemes differed in terms of how they packed the data for each arbitrarily shaped video object into packets. An experimental testbed was constructed to compare the performance of the different schemes. The experiments showed that the scheme in which no effort is made to maximise the amount of data in the packet performs worse than the others in terms of the amount of overhead it generates and the video quality obtained when it is used to stream content. The other schemes did exhibit small differences in terms of the amount of overhead generated and video quality obtained, but the differences were not sufficiently large to be able to identify any as being clearly better than the others.

This work describes a detailed simulation-based study of the performance of an IEEE 802.11e Medium Access Control (MAC) layer over an IEEE 802.11g Physical (PHY) layer. The study focuses on the number of simultaneous bidirectional G.711 Voice over IP (VoIP) calls that can be supported by a Wireless Local Area Network (WLAN) using the Extended Rate PHY - Orthogonal Frequency Division Modulation (ERP-OFDM) mode of 802.11g.A new scheme for adapting the WLAN MAC parameters is proposed in this work. The new scheme dynamically adapts the Contention Window (CW) based on the retransmission rate of the system. In addition, an adaptive Transmission Opportunity (TXOP) mechanism aids in balancing the uplink and downlink traffic levels and so provides the equality in uplink and downlink performance that is required for bidirectional VoIP traffic. The proposed scheme can thus maintain acceptable levels of QoS for higher call capacities, increasing the overall VoIP capacity of the system.