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3G and Beyond, 2005 6th IEE International Conference on

Date 7-9 Nov. 2005

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Displaying Results 1 - 25 of 95
  • MIMO-OFDM: Basic Relations between Coding, Spreading, Multicarrier and Singlecarrier Transmission

    Page(s): 1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (59 KB)  

    This contribution considers the basic relations between coding, spreading, multicarrier and singlecarrier transmission against the background of MIMO-OFDM. MIMO-OFDM is taken, because it can be regarded as a scheme which contains many others as special cases, and also because of its increasing relevance for future wireless communication. It is shown that spreading plays a central role: Spreading in space, time and frequency can be considered as the most general form of linear space-time-frequency-coding. Additionally it is demonstrated that spreading can be used to transform multicarrier transmissions into singlecarrier transmissions. Moreover, fading channels can be transformed in nonfading ones. This will be demonstrated for the case of Rayleigh fading channels with additive gaussian noise, which become simple gaussian channels. After an introduction and a short description of MIMO-OFDM, the concept of spreading and despreading is explained. It is shown, how spreading produces diversity which can be exploited at the receiving side. If no knowledge about the MIMO channel is available at the transmit side, i.e. if no backward channel can be used, this is an excellent means to cope with frequency- and/or time-selective channels. It is also shown what conventional channel coding can do in this context and what this means at the receiving side. Coding at the transmit side is concatenated with spreading and the MIMO channel. This results in a potential, that can be exploited by iterative detection schemes (turbo equalization/decoding). Simulation results are presented to underline the relevance of theoretical derivations. View full abstract»

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  • Exploitation of Diversity in MC-CDMA Systems

    Page(s): 1 - 5
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    MC-CDMA has an additional degree of freedom to exploit diversity compared to OFDMA or MC-TDMA due to spreading. This paper analyzes the achievable BER lower bounds for different MC-CDMA schemes exploiting channel state information (CSI) at the transmitter, the receiver, or both. Using channel knowledge at both sides is referred to as combined-equalization. Different design criteria for single-user combined-equalization are investigated and the corresponding lower bounds are derived. It is shown that the new lower bounds for combined-equalization outperform the known lower bounds for MC-CDMA systems which exploit CSI only at the transmitter or receiver. View full abstract»

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  • Adaptive MIMO-OFDM for Future Mobile Radio Communications

    Page(s): 1 - 4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (387 KB)  

    This paper addresses the topic of bit and power loading in coded MIMO-OFDM systems. Due to the need of designing communication systems with high spectral efficiencies, the combination of multiple antennas at transmitter and receiver with OFDM represents a promising approach. Moreover, channel knowledge at the transmitter can be exploited to adapt the transmission to the channel. While loading strategies for the uncoded case as well as the information theoretical solution are already known, the optimum scheme is still unknown for coded systems. In this paper, we compare different loading approaches for coded systems with respect to their error rate performance. View full abstract»

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  • Exploiting Multiuser Diversity for MIMO Cellular Systems Using Packet Scheduling and the VBLAST Receiver

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2509 KB)  

    Several packet scheduling techniques for the downlink of a multiple-input multiple-output (MIMO) cellular system are investigated. The system capacity for three scheduling are investigated. The system capacity for three scheduling algorithms, the conventional round robin scheduling (RRS) the antenna-assisted round robin (AA-RRS) and a novel VBLAST AA-RRS, are evaluated. Computer simulations are used to compare these scheduling schemes in terms of the expected and outage capacities. The novel scheme has proven to be beneficial for the system performance. View full abstract»

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  • Evaluation of the Capacity of Multiple-Access MIMO Schemes with Feedback in a Small Outdoor Cell

    Page(s): 1 - 5
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    Three algorithms to exploit the multi-user MIMO channel are examined and their system capacity evaluated in the uplink of a small urban cell scenario using measured channel data. An iterative scheme to determine transmit weights that achieve the system-wide Nash Equilibrium (NE) is compared to schemes achieving block-diagonalization (BD) of the overall system channel matrix and successive diagonalization (SD) among users. The BD scheme is shown to noticeably outperform the NE at high SNR - by as much as 9.7bps/Hz(44%) at 20dB SNR, whilst the SD yields as little as 33% of the capacity of BD. SD is, however, completely non-iterative which could be important in rapidly changing environments. The NE is found to sometimes yield a higher system capacity with more users; the setup examined here shows a rise of about 2bps/Hz in the system capacity when going from 3 users to 4. We also find that NE converges quickly, usually in fewer than 6 iterations, and reliably, more than 99% of the time, but BD can have serious slow-convergence problems. View full abstract»

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  • Heading Routing Protocols: Mobility-Based Routing for Ad-Hoc Networks

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (3962 KB)  

    In this paper, we present routing algorithms for mobile ad-hoc networks, which exploit the mobility patterns of nodes to provide a robust and long-lived route to destination and reduce flooding and overhead in the network. In the proposed protocols, only a small number of the network nodes are selected based on their Heading Direction Angle (HDA), to form a route from the source to the destination node. These approaches give solutions to some of the problems encountered in ad hoc networks, such as handling the frequent changes in the network topology due to mobility; maintaining the long-lived multi-hop paths between two communicating nodes. The obtained results show how these algorithms reduced the overhead and flooding in the network, and increased the life of the route in comparison with other routing protocols, such as Ad hoc On-demand Distance Vector (AODV). The new three approaches discussed in this paper could be applied to other routing protocols for mobile ad hoc networks in order to improve the performance of these protocols. View full abstract»

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  • Investigation of Energy Efficiency for Singlehop and Multihop Routing Shcemes in a Wireless Sensor Network

    Page(s): 1 - 4
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    Wireless sensor nodes run on small battery power and it is sometimes impossible to replace the batteries due to the environment and cost factors associated with them. Therefore, energy efficiency is a critical issue in the design and management of a wireless sensor network. In this paper, following the configuration and protocol implementation within a wireless sensor network, energy efficiencies for different routing schemes have been analysed based on the testing results on both energy consumption and data yield (throughput) for the whole network. The real world tests show that for a dense deployment multihop transmission is more energy efficient compared to singlehop transmission, while the opposite may be true when the sensors are deployed sparsely. View full abstract»

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  • Cooperative Diversity in Wireless Networks

    Page(s): 1 - 5
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    An ad-hoc network with a base station, a mobile and a third station acting as a relay is analysed. The channels are modelled using path loss, Rayleigh fading and thermal noise. Different combining methods and diversity protocols are compared. In the simulations, the amplify and forward protocol shows a better performance than the decode and forward protocol. To combine the incoming signals the channel quality should be estimated as well as possible. Information about the average quality shows performance benefits, and a rough approximation about the variation of the channel quality increases the performance even more. Whatever combination of diversity protocol and combining method is used, second level diversity is observed. The relative distances between the relay and the stations has a large effect on the performance. View full abstract»

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  • Relay Transmit Power Control In Cellular Multi-Hop Networks

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2806 KB)  

    In cellular multi-hop networks relay stations (RSs) are used to forward transmissions between the base station (BS) and user equipment (UE). The power at which the RS transmits not only determines which UEs it can serve but also the spatial separation at which another RS can reuse the same channel. It therefore jointly controls the routing and the medium access control (MAC) decisions. This means the optimal selection of the RS transmission power, which will be different for each target UE, is critical in realising the full benefits of a multi-hop system. In this paper we propose and evaluate a RS transmission power control (TPC) scheme that jointly considers the routing and MAC issues. We compare the capacities obtained from it to those obtained for a fixed RS transmit power case so as to infer relative benefits. View full abstract»

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  • Mobile Agents Based Congestion Aware Routing in Mobile Ad Hoc Networks

    Page(s): 1 - 7
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2168 KB)  

    This paper proposes a Mobile Agent based Congestion Aware Routing (MACAR) protocol, for routing in Mobile Ad Hoc Networks (MANETs). Here mobile agents collect network connectivity information based on congestion state and disperse this information across the network. This allows the nodes in the network to make "congestion aware decisions" during route discovery and route maintenance phases. The congestion state is measured based on the interface queue size and MAC drops at each node. In traditional on-demand routing protocols, "shortest path" is used as the metric in choosing and maintaining routes. MACAR chooses routes based on congestion as the primary metric. This results in a spatial distribution of traffic in the network and reduces congestion in the network. MACAR uses Ad Hoc On-Demand Distance Vector (AODV) routing as the underlying protocol [5]. MACAR and AODV protocols are compared through extensive simulations. Network throughput, end-to-end delay and routing overhead are the performance parameters considered. Results show that the robust routes provided by MACAR when compared to traditional on-demand routing protocols results in substantial reduction in end-to-end delay and improvement in network throughput. View full abstract»

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  • Robust GOB Intra Refresh Scheme for H. 264/AVC Video Over UMTS

    Page(s): 1 - 4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (3024 KB)  

    3G mobile system are designed to provide multimedia services. To fulfill QoS requirements for video applications, a robust video codec should be employed. In this paper, a robust and effective algorithm for Group of Blocks (GOB) Intra refresh in H. 264/AVC is presented. The objective is to mitigate the error propagation and improve the perceptual video quality over the mobile networks. Experimental results show that the proposed algorithm can efficiently improve the video quality when errors occur. View full abstract»

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  • Ultra-Fast 3G Videotelephony Session Setup

    Page(s): 1 - 3
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (3031 KB)  

    The establishment of a typical 3G videotelephony (video calls) session is a process that lasts typically around 5 to 8 seconds between today's deployed 3G video-call enabled terminals. This delay is exclusive of call signalling, and is due to the need to complete several protocol procedures as prescribed by the ITU-T H.324 standard and its annex C, including mobile level detection and H.245 messaging to open logical channels and define multiplexing modes. This paper presents AnswerFast Plus (AF+), a technique that significantly accelerates the 3G videotelephony session setup to make it almost as fast as voice calls (1 second or less). AF+ establishes a video telephony session in a ¿ round-trip duration of information transmission on the bearer channel, which is the minimum that can be achieved, while maintaining the flexibility of exchanging terminal preferences. AF+ offers major benefits not only from a user experience point of view, but also in terms of minimising infrastructure overheads, and reducing subscribers billing concerns. Another important advantage of AF+ is its interworking with deployed handsets. Because it is a 3G circuit-switched bearer based technology, and because AF+ information appears as noise to terminals that do not support it, it has an unmatched interworking record with existing deployed terminals. Extensive experiments on live 3G networks in a number of countries have been conducted and confirm our claims. View full abstract»

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  • Multimedia Broadcast Multicast Services: Concept & Capabilities

    Page(s): 1 - 4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (3827 KB)  

    Being one of the first 3G operators in the world with early UMTS experience, 3 were able to focus immediately on the UMTS opportunities and the challenges ahead, resulting in 3 being one of the early drivers for Multimedia Broadcast Multicast Service (or MBMS). This paper provides a brief history regarding the drivers for MBMS. The paper moves on to explain why the architecture is defined as it is today, including the challenges associated with rolling out an MBMS enabled network and some key service opportunities identified for MBMS. In addition the paper presents an insight to the benefits that MBMS may provide for an increasingly busy 3G network and ends with a discussion on how MBMS may compliment future technologies. View full abstract»

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  • Transmission Power Saving Methods for Multimedia Broadcast/Multicast Services in UMTS Networks

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (475 KB)  

    In current 3GPP R6 MBMS specifications, multimedia services are expected to be multicast/broadcast to all users or groups of users within the cell range. MBMS Counting Mechanism intends to analyse whether is more economic to transmit the multimedia services in a Point to Point (PtP) or Point to Multipoint (PtM) mode, evaluating in terms of radio resources management if it is preferable to use a single common channel reaching down the cell edge or single dedicated channels allocated to each user which conveys identical MBMS content. Macro Diversity Combining (MDC) is proposed as an enhancement for the MBMS standards, this method is proposed as a way to improve the received signal quality and at the same time increase the network coverage with considerable gains at radio resources availability. View full abstract»

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  • Soft Decode and Forward Improves Cooperative Communications

    Page(s): 1 - 4
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    Mobile receivers can benefit from an increased spatial diversity through cooperation. Two relaying techniques are typically used: either Amplify and Forward (AF) or Decode and Forward (DF). This contribution presents a new technique which combines the main advantages of both AF and DF. This technique amounts to a DF scheme where all operations are performed in a soft-input soft-output fashion. The relay performs a soft decoding of the received signal and reencodes it softly, that is incorporates reliability information about the decoded data. Simulations show that this Soft-DF scheme outperforms both AF and DF. View full abstract»

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  • Sequential Decoding for Mobile Receivers

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (97 KB)  

    Currently many classical detection and decoding algorithms receive new attention in mobile communications. Amongst those classics are low density parity check codes [1], concatenated codes [2], weighted decoding with log-likelihood values as well as soft-in/soft-out decoding as performed by the BCJR algorithm and its derivatives [4], [5]. All four classics show up as key elements in the so-called turbo decoding which first was invented by Berrou et al. in [6] as an iterative scheme to decode parallel concatenated codes. Later it was recognized that this scheme, namely iterative decoding by exchanging extrinsic values between two or more decoders, is a general principle named the "Turbo Principle" [5]. In this talk we will revive another classical decoding method called sequential decoding in order to use it for iterative decoding in high memory situations. For iterative detection/decoding (turbo) schemes in mobile receivers we modify sequential decoding which contrary to APP (BCJR) decoding enjoys a complexity almost independent from the number of states. This novel LISt-Sequential (LISS) decoder avoids most of the drawbacks of the classical sequential decoders such as variable work load and erased frames when working within a turbo scheme. It uses are a metric containing a priori and channel values, a metric length bias term for speeding up the tree search, a soft extension of paths without increasing the stack size and soft weighting to obtain a soft output. We present several mobile turbo applications using the LISS including equalization, single antenna interference cancellation, multiuser and MIMO detection. View full abstract»

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  • Interference Suppression in UTRA FDD Downlink Handover Regions

    Page(s): 1 - 5
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    It is known that significant multi-access interference is generated in a handover region in UTRA FDD downlink, particularly when both the Node-Bs involved in a handover are fully loaded. This paper investigates the use of blind minimum output energy (MOE) adaptive detector for suppressing this multi-access interference. A simple solution to the mismatch problem of the MOE detector is also proposed in the form of closed loop power control (CLPC). It is shown that a significant gain of 1.5 - 2.5 dB in average transmit power can be achieved by the use of adaptive interference mitigating detectors over the conventional Rake receiver. A requirement for the use of adaptive minimum mean square error (MMSE) detectors is the use of short scrambling sequences, which is not supported by current 3GPP specifications for the downlink but the impressive gains achieved by these adaptive detectors make a strong case for the incorporation of short scrambling sequences in the downlink for future UTRA evolution. View full abstract»

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  • Forward-link Interference in CDMA-Based Cellular Networks

    Page(s): 1 - 5
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    In this paper we have studied the in-band interference power caused by macro-cell base stations of a CDMA based cellular network. The impact of macro-cell load, location of the target receiver, service data rate of macro-cell users, and the number of sectors, on the average and standard deviation of the received interference power at a target receiver that works in the same frequency band of macro-cell base stations, is investigated. It is shown that the standard deviation of interference has a direct relation to the number of sectors as well as the data rate of service and an inverse relation to the distance of target receiver from base station. These results are then used to address a practically interesting issue, which is the utilisation of additional micro-cells working in the same band that existing macro-cells work. The achievable throughput at such micro-cells is calculated and backed by simulation. The results show that even in locations close to the macro-cell base station, in which the average interference is high, there is a possibility to sent data from micro-cell base station to users in the same frequency band. View full abstract»

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  • Blind Timing Synchronization for Filter-Bank Multicarrier Wireless Communications

    Page(s): 1 - 5
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    We describe the performance of a blind timing recovery algorithm for filter bank multicarrier modulation (FBMCM) modems. Our starting point is a the maximum-likelihood criterion. From that, we present the derivation of a closed-loop tracker and demonstrate how to derive a relatively low-complexity scheme with reasonable performance loss. Unlike previously published works, a remarkable acquisition range equal to plus and minus one half the FBMCM signaling interval is achieved. We also show by simulation a significant robustness with respect to the multipath channel and non ideal carrier frequency estimation. View full abstract»

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  • Improvements for the IPv6 Access Network Protection Protocols in Wireless Environments

    Page(s): 1 - 4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1126 KB)  

    Every user that joins a wireless access network to connect to the Internet expects to receive a secure and reliable service. The process of discovering other nodes on the same link as well as the recovery of routing information is known as Neighbour Discovery Protocol (NDP) [1] and until recently little attempt was made to protect it from misuse and attacks. The recently suggested protection methods for the routing mechanism of an IPv6 access network are not extensively tested and security vulnerabilities exist that can jeopardise the security of the provided services or even the integrity of the communicated information. By implementing the protocols for the protection of the router and neighbour discovery the research carried out identifies the potential vulnerabilities and suggests ways to protect against them. View full abstract»

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  • IPv6-Based Architecture for Fast and Cost-Effective Micro-Mobility Management

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (5831 KB)  

    To improve mobility management in all IPv6-based wireless networks, optimisation work on Mobile IPv6 (MIPv6) is being standardised. The Hierarchical MIPv6 (HMIPv6) and the Fast Handovers for MIPv6 (FMIPv6) have emerged as the two most promising protocols. However, the optimal integration of both schemes, together with mobility-aware QoS (quality of service) management, remains an open research issue. Furthermore, the current standard IPv6 address auto-configuration is not optimised for mobility contexts and thus is the bottleneck to real fast handoffs. In addition, out-of-order packets are generated at a mobile host when both FMIPv6 and HMIPv6 are applied jointly, degrading the QoS of ongoing sessions. To solve these problems, we propose IPv6-based micro-mobility architecture, where HMIPv6 and FMIPv6 are enhanced effectively and integrated efficiently. The simulation results demonstrate that the proposed architecture is the most cost-effective solution among three schemes based on the combination of HMIPv6 and FMIPv6 and can achieve faster handoffs compared with FMIPv6. View full abstract»

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  • TCP Performance Over UMTS Dedicated Channels with Finite RLC Buffer Size

    Page(s): 1 - 5
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    In this paper, simulation results are presented to demonstrate the effects on the performance of a TCP connection over a UMTS dedicated channel when the size of the Acknowledged Mode Radio Link Control (AM-RLC) data buffer at the Radio Network Controller is finite. The consequence of this restriction is that buffer overflow can occur. The TCP flavour (Tahoe, Reno, New Reno or SACK), FTP file size, RLC buffer size and DCH data rate are varied independently to map the effects of buffer size on the link throughput. The results are used to demonstrate how small changes in the RLC buffer size can have a significant impact on TCP throughput and that this impact varies considerably with TCP flavour. Explanations for the differing behaviours are examined in detail throughout the paper, before summarising with the overall conclusions. View full abstract»

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  • Inter-Operator Cooperation Challenges in SIP-Based Service Architecture of IP Multimedia Subsystem of UMTS

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (4688 KB)  

    One of the benefits of the evolution of the third generation mobile systemss such as UMTS (Universal Mobile Telecommunications System) toward the all-IP network architecture is to provide functionalities to support real-time multimedia services. Simple and efficient multimedia session handling characteristics of the Session Initiation Protocol (SIP), candidates it by 3GPP (Third Generation Partnership Project) for the signalling protocol of IP Multimedia Subsystem (IMS) of UMTS. An important issue in IMS is the fact that service control procedures of the subscribers are performed in the home network. In this paper we review the SIP-based service registration and session establishment procedures in IMS and we study the challenges for providing a SIP-based cooperative mechanism between network operators of different subscribers in IMS in order to prevent extending of service control procedures of roamers to home network and to optimize the session establishment procedure by performing service control procedures of roamers in the visited network. View full abstract»

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  • VoIP Applications over WLAN with Multistage Interference Cancellation Smart Antennas

    Page(s): 1 - 5
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    In order to improve the transmission quality of wireless local area network (WLAN), incorporation of emerging technologies is required. Smart antennas, as one of the key technologies in future communications, can significantly improve the Signal-to-Interference-plus-Noise ratio (SINR) and hence reduce the transmission errors. Because WLAN uses the unlicensed industrial, scientific, and medical (ISM) radio bands, strong cochannel interference (CCI) sources from systems other than WLAN can significantly degrade the throughput of WLAN and result in various transmission problems, such as latency, jitter, and packet loss. These problems usually render performance degradation of Voice over IP (VoIP) services. The CCI from uncoordinated sources also lead to slow convergence of smart antennas using data-dependent adaptive algorithms. This work demonstrates that applying low cost Multistage Interference Cancellation Smart Antennas (MICSA) to WLAN conducts superior interference suppression and better performance improvement of VoIP services compared with using conventional single stage smart antennas to WLAN. View full abstract»

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  • Slow Frequency Hopping Assisted MC DS-CDMA Using Large Area Synchronised Spreading Sequences

    Page(s): 1 - 5
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    The family of Multi-Carrier Direct-Sequence CDMA (MC DS-CDMA) systems exhibits numerous attractive properties, which render them attractive candidates for next-generation wireless communications. We demonstrate that spreading codes exhibiting a so-called interference-free window (IFW) are capable of outperforming classic spreading codes, when the interfering multi-user and multipath components arrive within this IFW. The best possible quasi-synchronous timing of the spreading sequences has to be adjusted with the aid of accurate adaptive timing advance control, which has to be significantly more accurate than that used in the lower-bit-rate second-generation GSM system. Firtunately, the IFW duration may be extended with the advent of multi-carrier DS-CDMA proportionately to the number of subcarriers. Hence the resultant MC DS-CDMA system is capable of exhibiting a near-single-user performance without employing a multi-user detector. A deficiency of the resultant system is that the number of spreading codes exhibiting a certain IFW is limited and so is the IFW duration. This contribution sets out to mitigate the above-mentioned shortcomings so that when the users' delays are in the range of the IFW, we separate them with the aid of the unique, user-specific LAS spreading codes. By contrast, when the users roam at a high distance from the base-station and hence their received signal arrive outside the range of the IFW, we separate them using their unique frequency hopping patterns. View full abstract»

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