Benny Bing

Spatiotemporal Sensing in Cognitive Radio Networks

Cognitive radio networks need to continuously monitor spectrum to detect the presence of the licensed users. In this paper, we have exploited spatial diversity in multiuser networks to improve the spectrum sensing capabilities of centralized cognitive radio (CR) networks. We develop a fixed and a variable relay sensing scheme. The fixed relay scheme employs a relay that has a fixed location to help the cognitive network base station detect the presence of the primary user. The variable relay sensing scheme employs cognitive users distributed at various locations as relays to sense data and to improve the detection capabilities. This effectively reduces the average detection time by exploiting spatial diversity inherent in multiuser networks. Finally, we study the network outage probabilities to compare the performances of the fixed and variable relay schemes.

A call admission control scheme using genetic algorithms

Next Generation Wireless Systems (NGWS) will provide a variety of services to mobile users including high speed data, real-time applications and real-time multimedia support with a certain quality of service (QoS) level. An efficient handoff management is one of the key issues in order to support global roaming of the mobile users among different network architectures of the NGWS.In this paper, a new call admission control scheme, Genetic-based call admission control (GAC), is proposed for NGWS. The GAC scheme uses genetic algorithms to achieve high network utilization, minimum cost, minimum handoff latency and mobile terminals (MT) QoS requirements. Performance analysis is provided to assess the efficiency of the proposed GAC scheme. Simulation results show a significant improvement in handoff latencies and costs over the heuristic approach and other CAC schemes.

Securing the download of radio configuration files for software defined radio devices

Radio configuration (R-CFG) files for software defined radio (SDR) devices can be downloaded over the air, allowing these devices to support multi-mode functionality using a single transceiver. SDR device manufacturers are likely to provide the R-CFGs, which may contain proprietary information. In such cases, it is necessary to secure the server/SDR device connection during the R-CFG download. Therefore, a protocol to securely connect manufacturers server and SDR devices, called LSSL, is proposed. The LSSL is a lightweight protocol based on the SSL protocol, but it takes up less bandwidth, thus, it is more suitable for SDR handheld devices operating under low-capabilities, low-bandwidth and error-prone wireless links. However, securing the R-CFG download connection does not guarantee that a valid R-CFG, that is, an R-CFG that has been approved by the regulatory agency, has been downloaded. In order to install only valid R-CFGs, a secure download protocol is presented. The secure protocol includes, besides the LSSL, steps of mutual authentication, public/private key mechanisms for data encryption and decryption, and fingerprint calculations to check data integrity. Finally, the secure protocol is analyzed and shown to be deadlock and livelock-free, and to properly terminate. Experiments using Java 2 Micro Edition (J2ME) are performed to compare the LSSL and the SSL, and to demonstrate the feasibility of the secure protocol.

MPEG-4 Bandwidth Prediction for Broadband Cable Networks

In this paper, we analyze the bandwidth requirements of MPEG-4 and propose and evaluate the accuracy of two new MPEG-4 video traffic models. The first predicts the size of the B-frame while the second predicts the size of the group of pictures (GOP). In a broadband cable network, the B-frame prediction model can be employed by a cable headend to provision video bandwidth efficiently or more importantly, reduce bit rate variability and bandwidth requirements via selective B-frame dropping, thereby minimizing buffering requirements and packet losses at the set top box. It will be shown that the model provides highly accurate prediction for a wide variety of video types, in particular, high action and regular movies encoded in high quality resolution. This is an important benefit since high motion MPEG videos demand the highest bandwidth and generate the widest range of bit rate requirements. Although the B-frame prediction model is very simple to implement, this paper also proposes two methods to simplify its operation further without sacrificing prediction accuracy. We then enhance the B-frame and GOP prediction models using a new scene change detector metric.

A fast and secure framework for over-the-air wireless software download using reconfigurable mobile devices

OTA software download is an enabling technology that leverages on the flexibility of radio hardware. With dynamic OTA download, mobile devices can connect to any type of wireless network, download the required radio software, and reconfigure on demand. This article covers two key system design issues: delta compression and security

Advanced mouse pointer control using trajectory-based gesture recognition

In this paper, a method to control the movement of a mouse pointer using simple hand gestures and a webcam is proposed. A real-time tracking algorithm is implemented based on adaptive skin detection and motion analysis. Using the history of motion, the trajectory of the movement of the hand is drawn and then used to identify a gesture. A region of interest algorithm is proposed, in order to scale the motion when the user is located far away from the point of capture. The motion of the mouse pointer is scaled accordingly. Demonstrations using our prototype clearly illustrate the benefits of our system.

Cross-Layer Congestion Control and Scheduling in Multi-Hop OFDMA Wireless Networks

In this paper, we consider joint end-to-end congestion control and multiuser scheduling in multi-hop wireless networks, where orthogonal frequency-division multiple access (OFDMA) is the air interface. Compared to its single-channel counterpart, this problem is significantly more challenging because subchannel assignment and power allocation for all nodes and network traffic need to be jointly optimized. To avoid co-channel inference, we first consider an OFDMA subchannel separation problem in multi-hop communication scenarios. Then, we address this cross-layer optimization problem by decomposing it into two subproblems: a TCP layer congestion control for traffic allocation and a weighted scheduling for OFDMA subchannel assignment and power control. Observing that the scheduling for multiuser OFDMA in multi-hop wireless networks is inherently NP-hard, we propose a low-complexity algorithm that ensures a solution converging to the optimum. The performance of the algorithm is demonstrated through simulations.

An efficient reservation MAC protocol with preallocation for high-speed WDM passive optical networks

Wavelength division multiplexing passive optical networks (WDM PONs) can dynamically offer each end user a unique optical wavelength for data transmission as well as the possibility of wavelength reuse and aggregation, thereby ensuring scalability in bandwidth assignment. In this paper, we propose a new byte size clock (BSC) reservation MAC scheme that not only arbitrates upstream transmission and prevents optical collisions, but also varies bandwidth according to demand and priority, reduces request delay using pre-allocation and delta compression, and handles the addition/reconfiguration of network nodes efficiently. The new access scheme exploits both WDM and TDM to cater for both light and heavy bandwidth requirements and supports both Ethernet and ATM packets without segmenting or aggregating them. Our proposed protocol is not only backward compatible with APON and EPON, but also provides a better utilization of the access link in terms of the throughput and delay. In addition, the amount of pre-allocated bandwidth can be minimized using delta compression, which in turns reduces the latency due to the request and grant mechanism. We analyzed, evaluated, and simulated the performance and practicality of the proposed scheme.

Stabilization of the randomized slotted ALOHA protocol without the use of channel feedback information

This paper examines the dynamic characteristics of the randomized slotted ALOHA (RSA) protocol that is commonly employed in contention-based reservation multiaccess schemes. The average drift (or expected packet flow) is derived from a Markov chain for a finite number of single-buffer users and is used to determine the stability of the protocol. Results show that unlike many random access schemes (RSA) possesses exactly one equilibrium point even when the channel load estimate is inaccurate. However, any under-estimation in the channel load increases the equilibrium backlog (and reduces the average throughput) at a rate faster than when the channel load is overestimated. The protocol can achieve stable, nonzero throughput without the need for channel feedback information.

An adaptive subchannel allocation algorithm for OFDM-based wireless home networks

We present a novel, adaptive subchannel allocation algorithm for the downlink channel of a multiuser, OFDM-based wireless home network. Since channel resources are not adaptively allocated in a traditional OFDM system, some of the users with fixed frequency channel allocation may experience deep fading in a frequency-selective multipath environment. This problem can be mitigated using an adaptive algorithm, which can be modeled as an optimization problem that allocates the proper number of subchannels to achieve maximum channel capacity. We employ the classical bipartite matching algorithm to achieve optimal OFDM subchannel allocation. Simulation results show that the total capacity increases remarkably, and that higher channel capacity is achieved when the number of users is increased. In a wireless environment, the reallocation overhead can be large. As such, we propose a hybrid method for subchannel allocation to support more users while reducing the reallocation overhead. We simulated the performance of the hybrid algorithm and compared it with the matching-only algorithm.