• Performance analysis of an improved power-saving medium access protocol for IEEE 802.11 point coordination function WLAN

      Safdar, Ghazanfar Ali; Scanlon, W.G. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2006)
    • Performance analysis of energy detection over hyper-Rayleigh fading channels

      Chatziantoniou, Eleftherios; Allen, Ben; Velisavljević, Vladan; University of Bedfordshire (IET, 2015-01-01)
      This study investigates the performance of energy detection (ED)-based spectrum sensing over two-wave with diffused power (TWDP) fading channels, which have been found to provide accurate characterisation for a variety of fading conditions. A closed-form expression for the average detection probability of ED-based spectrum sensing over TWDP fading channels is derived. This expression is then used to describe the behaviour of ED-based spectrum sensing for a variety of channels that include Rayleigh, Rician and hyper-Rayleigh fading models. Such fading scenarios present a reliable behavioural model of machine-to-machine wireless nodes operating in confined structures such as in-vehicular environments.
    • Performance analysis of novel randomly shifted Certification Authority Authentication Protocol for MANETs

      Safdar, Ghazanfar Ali; O'Neill, M.P. (Hindawi, 2009-01)
      The provision of security in mobile ad hoc networks is of paramount importance due to their wireless nature. However, when conducting research into security protocols for ad hoc networks it is necessary to consider these in the context of the overall system. For example, communicational delay associated with the underlying MAC layer needs to be taken into account. Nodes in mobile ad hoc networks must strictly obey the rules of the underlying MAC when transmitting security-related messages while still maintaining a certain quality of service. In this paper a novel authentication protocol, RASCAAL, is described and its performance is analysed by investigating both the communicational-related effects of the underlying IEEE 802.11 MAC and the computational-related effects of the cryptographic algorithms employed. To the best of the authors' knowledge, RASCAAL is the first authentication protocol which proposes the concept of dynamically formed short-lived random clusters with no prior knowledge of the cluster head. The performance analysis demonstrates that the communication losses outweigh the computation losses with respect to energy and delay. MAC-related communicational effects account for 99% of the total delay and total energy consumption incurred by the RASCAAL protocol. The results also show that a saving in communicational energy of up to 12.5% can be achieved by changing the status of the wireless nodes during the course of operation.
    • Performance analysis of spectrum sensing techniques for cognitive radio

      Allen, Ben; Chatziantoniou, Eleftherios (University of Bedfordshire, 2006)
      Spectrum sensing is a key element for cognitive radio and is process of obtaining awareness about the radio spectrum in order to detect the presence of other users. In this paper we study the performance of different spectrum sensing techniques in terms of detection performance and required SNR, based on theoretical expressions. Keywords- cognitive radio; spectrum sensing; energy detection; matced filter detection; cyclostationary feature detection
    • Performance analysis of switched-sector antennas for indoor wireless LANs

      Pesik, L.J.; Beach, Mark; Allen, Ben; University of Bristol (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2001)
      Given the potential market for wireless LAN (WLAN) technology, capacity within the available 2 and 5 GHz frequency bands is likely to fall short of market demands. Multiple-sector antenna arrays are known to be able to provide capacity enhancement by means of interference reduction through spatial filtering. In this paper, the performance of an eight-element circular array acting as an Access Point (AP) in indoor wireless LAN environments is analysed. Spatial-temporal channel data used within the analysis were obtained from physical measurements within numerous indoor environments using a state-of-the-art wideband vector signal analyser. Performance analysis of the array employing a switched-sector controller within the Hiperlan/2 standard is appraised in terms of carrier-to-interference (C/I) ratios. Results show that an isolation of up to 15dB can be achieved between the two polarisations, by means of using an antenna array at the AP. It is shown that 54% of the time, 2 users per timeslot can be supported by the system
    • Performance analysis of UWB impulse radio with timing jitter

      Liu, J.; Chu, Xiaoli; Allen, Ben; Ghavami, Mohammad; King's College London (IET, 2006-04)
      UWB impulse radio communications can provide multi-path diversity when a rake receiver is used. The narrow time domain pulse can effectively combat the fading. Perfect pulse synchronisation is, however, required to obtain optimum performance. For a correlation receiver, small timing jitter between the reference pulse and the received pulse causes performance degradation. Analytical results for the performance degradation caused by timing jitter can be combined with a suitable channel fading probability distribution function to form a combined probability distribution for the received signal power at the output of the correlator. This paper analyses the statistical distribution of the received power at the output of a correlation receiver for a single pulse with timing jitter. By treating the power degradation due to timing jitter as a mathematical equivalence, it is shown that path diversity combining can be a potential technique to mitigate the timing jitter as well as the multi-path fading.
    • Performance assessment of terrestrial and satellite based position location systems

      Kothris, D.; Beach, Mark; Allen, Ben; Karlsson, Peter (IEE, 2001)
    • Performance comparison of differential space-time signalling schemes for OFDM systems

      Hashim, W.; Said, F.; Allen, Ben; Aghvami, A.Hamid; Ismail, A. F. (IEEE, 2005-11)
      Differential transmit diversity is an attractive alternative to its coherent counterpart, especially for multiple antenna systems where channel estimation is more difficult to attain compared to that of single antenna systems. In this paper we compare two different types of differential transmit diversity techniques for OFDM based transmissions. The first technique uses differential space-time block codes (DSTBC) from orthogonal designs and the second uses the differential cyclic delay diversity (DCDD). The results compare the bit error performance for several transmit antenna configurations. The results show that DCDD offers a very close performance to that of DSTBC, with the advantage of a simplified receiver structure.
    • Performance comparison of spatial diversity array topologies in an OFDM based wireless LAN

      Allen, Ben; Brito, Rodrigo; Dohler, Mischa; Aghvami, A.Hamid (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2004-05)
      Spatial diversity is well known to provide improved coverage and capacity for wireless systems. With the increasing demand for wireless LANs, the robust provision of its services to users is becoming increasingly important. This paper examines the performance of spatial diversity in an OFDM based wireless LAN for various antenna topologies. It is shown that a circular array topology at the access point provides the best performance when operating in an indoor office environment compared with linear and semi-circular topologies. It is also shown that such a configuration improves the service provision by more than 10 dB compared to a single antenna system.
    • Performance evaluation of a Bluetooth interference canceller in IEEE802.11b wireless networks

      Zeng, Z.; Allen, Ben; Aghvami, A.Hamid; King's College London (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2005-11)
      In this paper, we propose a narrowband interference canceller (NIC) to cancel Bluetooth interference occurring in IEEE 802.11b WLAN systems. The proposed NIC has a simple structure: an adaptive filter followed by a Rake receiver. The simulation results show that the proposed NIC can effectively cancel Bluetooth interference in an 802.11b receiver. Although an IEEE802.11b/Bluetooth framework is given as an example, the proposed NIC can be used in any spread spectrum system with frequency-hopping narrowband interference (FHNBI).
    • Performance evaluation of actual multielement antenna Systems under transmit antenna selection/maximal ratio combining

      Papamichael, Vasilis C.; Karadimas, Petros (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011)
    • Performance investigation of DS-CDMA detectors employing a dual polarised antenna

      Webber, Julian; Beach, Mark; Allen, Ben; Canagarajah, Nishan; University of Bristol (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2001)
      The benefits of polarisation diversity as a fade countermeasure within second generation cellular networks are well known. Capacity enhancement by means of joint detection is also a well-regarded technique for interference-limited systems such as TD-CDMA (time division-code division multiple access) within the UMTS (Universal Mobile Telecommunication System) wireless standards. However, relatively little attention has been focussed towards the potential gains of combining these two technologies. This paper considers, by means of a series of wideband dual polar channel measurements from a field trials campaign taken within the lower UMTS band (1910-1915 MHz), the relative merits of this approach when applied to a multistage interference canceller. This paper shows that signal strength improvements of between 2.5 dB and 3.2 dB at the 1% cumulative level were observed by applying dual polarised antennas at the receiver
    • Performance of a side-mounted PIFA in cluttered environment for GPS operation

      Ur-Rehman, Masood; Chen, Xiaodong; Parini, Clive G.; Ying, Zhinong (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012)
    • Performance of differential and differential unitary space-time block codes over spatially correlated Rayleigh fading channels

      Allen, Ben; Kuroda, Y.; Said, F.; Aghvami, A.Hamid; King's College, London (IET, 2004)
      This paper compares the performance of both differential space-time block codes (DSTBC) and differential unitary space-time block codes (DUSTBC) for multiple transmitters with one receiver over spatially correlated narrowband slow Rayleigh fading channels. It is shown that the relative performance of all candidate codes is improved when the number of transmit antennas is kept low. Improved performance is also observed when differential STBC are used compared to coherent STBC.
    • Phase-encrypted secure communication technique for GPONs

      Ajmal, Tahmina; Hugues-Salas, Emilio; Razavi, Rouzbeh; Quinlan, Terence; Zervas, George; Simeonidou, Dimitra; Walker, Stuart D. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007)
      The paper presents an FPGA-based physical layer phase-encryption technique suitable for applications in high speed passive optical networks. The macroscopic cryptography technique offers completely opaque communication over transoceanic distances, gigabit date rates and multiple wavelengths.
    • Pointer controlled power saving medium access control protocol for IEEE 802.11 infrastructure networks

      Safdar, Ghazanfar Ali; Scanlon, W.G. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2004)
    • Power loss modelling of short-range ultra wideband pulse transmissions

      Liu, Jiamin; Dohler, Mischa; Allen, Ben; Ghavami, Mohammad (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2006-02)
      Narrowband path loss models are not applicable to the link budget calculation of ultra wideband (UWB) signals. In the paper, a rigorous analysis reveals the power loss behaviour of short-range UWB pulse systems when operated in a rich multi-path environment. A novel breakpoint is derived that is within the vicinity of the transmitter, and is shown to influence the UWB link budget considerably. Furthermore, it is shown that the power delay profile does not generally follow a simple negative exponential dependency. Also, the effects of perfect and imperfect correlator onto the overall UWB pulse power loss are considered.
    • Prevention against threats to self co-existence - a novel authentication protocol for cognitive radio networks

      Safdar, Ghazanfar Ali; Albermany, Salah A.; Aslam, Nauman; Mansour, Ali; Epiphaniou, Gregory; University of Bedfordshire (IEEE, 2014-05)
      Cognitive radio networks are intelligent networks that can sense the environment and adapt the communication parameters accordingly. These networks find their applications in co-existence of different wireless networks, interference mitigation, and dynamic spectrum access. Unlike traditional wireless networks, cognitive radio networks additionally have their own set of unique security threats and challenges, such as selfish misbehaviours, self-coexistence, license user emulation and attacks on spectrum managers; accordingly the security protocols developed for these networks must have abilities to counter these attacks. This paper presents a novel cognitive authentication protocol, called CoG-Auth, aimed to provide security in cognitive radio networks against threats to self co-existence. CoG-Auth does not require presence of any resource enriched base stations or centralised certification authorities, thus enabling it to be applicable to both infrastructure and ad hoc cognitive radio networks. The CoG-Auth design employs key hierarchy; such as temporary keys, partial keys and session keys to fulfil the fundamental requirements of security. CoG-Auth is compared with IEEE 802.16e standard PKMv2 for performance analysis; it is shown that CoG-Auth is secure, more efficient, less computational intensive, and performs better in terms of authentication time, successful authentication and transmission rate.
    • Providing security and energy efficiency in wireless ad-hoc sensor networks through Secure Cluster-Head Election (SEC-CH-E)

      Garcia-Palacios, Emiliano; Mehallegue, Noureddine; Safdar, Ghazanfar Ali (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012)