Iftekhar Ahmad

Performance evaluation of IEEE 802.15.4 for mobile sensor networks

The IEEE 802.15.4 standard medium access control (MAC) protocol for low rate wireless personal area networks (LRWPAN) is design mainly for static sensor networks and its capability to support mobile sensor networks has not yet been established. To the best knowledge of authors, this is the first paper that evaluates the suitability of IEEE 802.15.4 MAC in mobile sensor networks environment. We evaluate the performance based on nodes speed and beacon order, and observe the effect on energy usage, packet delivery ratio and time required to associate with its coordinator. From the experiment we observe that the moving nodes experienced serious problems in association and synchronization and show results on energy usage, throughput , association and reassociation rate with different speeds of moving node. We also identify some key research problems that need to be addressed for successful implementations of IEEE 802.15..4 in mobile sensor networks environment.

A novel mobile WiMAX solution for higher throughput

The IEEE 802.16 standard, also known as WiMAX, has emerged as an exciting technology for broadband wireless communications with potentials to offer high throughput and support high bandwidth demanding applications. WiMAX, however, has yet to prove its effectiveness when the end terminals are not fixed and have the capacity to move from one place to another at different speeds. Recent studies suggest that while WiMAX (802.16e) has the potential to deliver a data rate up to 75 Mb/s for fixed wireless communications, it fails drastically for mobile wireless communications, often providing a data rate less than 1 Mb/s when the mobile nodes travel at high speeds, which offers a huge challenge for QoS management. Multipath fading that causes high bit error rate at the receiver end is a key reason for low throughput at high speed. Bit error rate and maximum packet size determine the packet error rate, and error recovery for higher number of corrupted packets is not always an attractive option for many real-time applications with delay and jitter constraints. In this paper, we propose a mathematical model to estimate the bit error probability when the mobile station travels at different speeds. The estimated value of bit error probability is then taken into account to proactively compute the appropriate maximum packet size that offers the best chance to achieve improved throughput at different operating conditions. We simulated the proposed scheme for a centralized video surveillance system in a public train where the train is the mobile node and sends real-time video data to the base stations. The results show that the proposed scheme achieves significantly higher throughput and lower jitter compared to other standard schemes.

Service Class Resource Management for Green Wireless-Optical Broadband Access Networks (WOBAN)

Exponential growth in the volume of wireless data, boosted by the growing popularity of mobile devices, such as smartphone and tablets, has forced the telecommunication industries to rethink the way networks are currently designed, and to focus on the development of high-capacity mobile broadband networks. In response to this challenge, researchers have been working toward the development of an integrated wireless optical broadband access network. Two major candidate technologies, which are currently known for their high capacity as well as quality of service (QoS) for multimedia traffic, are passive optical networks (PON), and fourth generation (4G) wireless networks. PON is a wired access technology, well known for its cost efficiency and high capacity; whereas 4G is a wireless broadband access technology, which has achieved broad market acceptance because of its ease of deployment, ability to offer mobility, and its cost efficiency. Integration of PON and 4G technologies in the form of wireless-optical broadband access networks, offers advantages, such as extension of networks in rural areas, support for mobile broadband services, and quick deployment of broadband networks. These two technologies however, have different design architectures for handling broadband services that require quality of service. For example, 4G networks use traffic classification for supporting different QoS demands, whereas the PON architecture has no such mechanism to differentiate between types of traffic. These two technologies also differ in their power saving mechanisms. In this paper, we propose a service class mapping for the integrated PON-4G network, which is based on the M/G/1 queuing model. We also propose a class-based power saving mechanism which significantly improves the sleep period for the integrated optical wireless unit, without compromising support for QoS. Results indicate that our proposed class-based power saving scheme reduces power consumption by up to 80%, and maintains the QoS within the requirements of the service level agreement.

High Utility Video Surveillance System on Public Transport Using WiMAX Technology

Video surveillance on public transport is a useful tool to fight against anti-social behaviour like vandalism, harassment, graffiti and terrorism. Real-time video surveillance on moving public transport faces serious technological challenges mainly due to limited throughput offered by existing communication technologies at high vehicular speeds. Success of real-time video surveillance on public transport heavily depends on future communication technologies like WiMAX. WiMAX has emerged as an exciting technology with promises to offer high throughput and improved quality of services (QoS), key requirements for video surveillance on public transport. WiMAX however, offers limited throughput at high vehicular speeds mainly because of multipath fading that causes high bit error rate at the receiver at vehicular speeds. In our previous works, we showed that it is possible to estimate the bit error rate at the receiver end at various vehicular speeds in WiMAX and accordingly, some proactive measures can be adopted to improve the throughput to some extents. Overall throughput however, may still be insufficient to support the streaming video data from all the cameras mounted on a public transport at high vehicular speeds. In this paper, we propose a new scheme that estimates utility for different cameras and puts some low utility cameras offline and thereby maintains high utility of the video surveillance system when the throughput at high vehicular speeds become insufficient. Simulation results confirm the effectiveness of the proposed scheme.

A Segregation Based MAC Protocol for Real-Time Multimedia Traffic in WLANs

Providing quality of service (QoS) for multimedia applications in wireless local area networks (WLAN) is a very challenging task. This is mainly due to the real-time nature of multimedia traffic such as voice and video applications, that are sensitive to delay and jitter. QoS guarantees for real-time traffic must be imposed in WLAN so as to enable WLAN users to fully benefit from multimedia applications. The current medium access control (MAC) protocol that is widely used is the legacy IEEE 802.11, but this protocol does not support QoS for realtime traffic. To enhance the legacy 802.11, the IEEE 802.11e protocol was introduced to support QoS through prioritization of traffic. The 802.11e introduces a new co-ordination function known as hybrid coordination function (HCF). In this paper we study the performance of multimedia traffic in the legacy 802.11 and 802.11e and propose a technique to improve realtime traffic in multimedia applications by traffic segregation. We show that segregation of multimedia traffic improves delay and jitter performance of real-time traffic.

Providing QoS for Symmetrical Voice/Video Traffic in Wireless Networks

Voice over IP (VoIP) and voice-video over IP (VIoIP) are becoming very popular and widespread. These types of real-time services produce streams that are almost symmetrical in nature. A new token passing media access control (MAC) developed by our group, called wireless token network (WTN), has been designed with QoS guarantees in mind. We have previously shown in our previous paper (2006) that WTN supports a higher number of VoIP clients compared to 802.11e due to its higher channel efficiency. In this paper we show that WTN also provides superior QoS for bidirectional streams such as VIoIP due to a higher proportion of channel access given to the access point (AP). Performance results are generated by benchmarking WTN against IEEE 802.11 DCF, IEEE 802.11e EDCA and SpectraLink SVP MAC protocols. These results show that whilst appropriate for unidirectional traffic, these current popular solutions do not provide QoS for streams in both directions, due to design constraints which treat the access point as a single client node.

Call Admission Control Scheme for Improved Quality of Service in WiMAX Communication at Vehicular Speeds

The IEEE 802.16e standard, also known as mobile WiMAX, has emerged as an exciting mobile wireless communication technology that promises to offer both high throughput and guaranteed quality of service (QoS). Call admission control (CAC) scheme serves as a useful tool for WiMAX, which ensures that resources are not overcommitted and thereby, all existing connections enjoy guaranteed QoS. Existing CAC schemes largely depend on readily available information like currently available resources and bandwidth demand of the new call while making an acceptance or rejection decision once a new request arrives. Since wireless channels are not as reliable as wired communication, CAC scheme in WiMAX communication faces a serious challenge of making a right estimate of the usable channel capacity (i.e., effective throughput capacity) while computing the available resources in various communication scenarios. Existing CAC schemes do not consider the impact of mobility at vehicular speeds when computing the usable link capacity and available resources. In this paper, we propose a new CAC scheme that estimates the usable link capacity for WiMAX communication at various vehicular speeds and uses this information while making a CAC decision. The proposed CAC scheme takes the speed distribution model of a mobile node into account during the CAC decision making process. Simulation results confirm that the proposed scheme achieves lower dropping rate and improved QoS compared to existing schemes.

An improved architecture for integrating Fourth Generation wireless and Passive Optical Networks

The necessity to support the rapidly growing high speed broadband services requires the use of latest technologies and quality of service (QoS) control techniques. Two such technologies include Fourth Generation (4G) wireless and New Generation Passive Optical Networks (NG PON). 4G communication technology encompasses both wireless and cellular systems, which aims to provide real-time voice, video and Internet services to the end user with high QoS. Moreover, it offers high throughput and supports mobility. A passive optical network (PON) is a reliable back haul technology, which can provide high bandwidth and is highly cost effective. The combination of 4G with NG-PON creates an access network that is cost efficient, reliable, flexible as well as facilitating mobility and ubiquity. However, this integration has many challenges such as maintaining the QoS of whole network. In this paper, we propose the NG PON as an alternative solution for the point to point fiber in the 4G centralized co-ordinated Multi-Point (COMP) transmission and reception. This architecture is for joint transmission downlink COMP which benefits from the broadcasting transmission in the downlink of PON. Moreover, it serves both fixed and mobile stations. The simulation compares the capital cost of using NG PON against point to point fibre in COMP architecture. The results reveal that up to 80 percent cost reduction can be achieved by using the proposed solution.

A proactive forward error control scheme for mobile WiMAX communication

The IEEE 802.16 standard, also known as WiMAX, has yet to prove its effectiveness when the end terminals are not static and free to move at vehicular speeds. High bit error rate caused by multipath fading at high vehicular speeds, is the key reason for low throughput at high speeds. Standard error control mechanisms like transmission control protocol (TCP) and forward error correction (FEC) have limited impact on the overall throughput at vehicular speeds. In this paper, we propose a proactive FEC scheme that adjusts the FEC code size based on the estimated bit error rate at various vehicular speeds. We show a mathematical model to estimate the bit error rate in WiMAX communication. We then propose a FEC scheme to proactively compute the FEC code size. We simulated the proposed scheme for a centralized video surveillance system in a public train where the train is the mobile node and sends real-time video data to the base stations. The results show that the proposed scheme achieves significantly higher throughput and lower jitter compared to existing schemes.

An Improved FEC Scheme for Mobile Wireless Communication at Vehicular Speeds

WiMAX has emerged as a promising wireless communication technology with potential to deliver high throughput and guaranteed quality of service to the end applications. Recent studies suggest that while WiMAX (802.16e) is capable of delivering a data rate of up to 75 Mbps for fixed wireless communications, data rate decreases drastically for mobile wireless communications, often providing a data rate less than 1 Mb/s when the mobile nodes travel at vehicular speeds. High bit error rate caused at high vehicular speeds is the key reason for low throughput. In noisy mobile communication environments, standard error control mechanisms like the transmission control protocol (TCP) has limited and often detrimental impacts on the overall throughput because of the excessive retransmission overheads. To address this issue, WiMAX standard incorporates forward error correction (FEC) mechanism that eliminates the need for retransmissions. In FEC, extra parity bits are added to the original message to recover the corrupted information. Adaptive FEC that adjusts the size of extra parity bits in response to packet retransmission requests is an enhancement over standard FEC that uses fixed block of party bits. Existing adaptive FEC schemes, however, have limited efficiency when the end terminal moves at vehicular speeds. In this paper, we propose a new FEC scheme that estimates and adjusts the size of extra parity bits to suit the channel conditions. We apply the concept of interval based data sampling to address the dynamic nature of communication environments at high vehicular speeds.