Efficient allocation of channels for wireless communication in different network scenarios has become an extremely important topic of recent research. The main challenge lies in the fact that the channel allocation problem is NP-complete. Because of a maximum allowable time limit imposed in practical situations for allocation of channels, sometimes we may need to be satisfied with a near-optimal solution. In this correspondence, we present a discussion on the various challenges and approaches that have been used by different researchers to solve the problem of channel allocation taking into account different interference issues and efficient utilization of available communication channels for cellular mobile (including multimedia communication) environment and cognitive radio based networks. Copyright © 2010 John Wiley & Sons, Ltd.

A survey on the channel assignment problem in wireless networks

In recent years, cellular networks have experienced an astronomical increase in the use of Short Message Service (SMS), making it a popular communication means for inter-personal as well as content provider-to-person usage. Yet little is known about the traffic and message user behavior in real SMS systems. In this paper, we present a measurement study of SMS based on traces collected from a nationwide cellular carrier during a three-week period. We characterize message traffic at both the message level and the conversation thread level. We also examine the "store-and-forward" mechanism of SMS and present initial measurements on how messages are actually delivered.

/pdf/a-study-of-the-short-message-service-of-a-nationwide-tqfkds5qwi.pdf

A study of the short message service of a nationwide cellular network

SMS has been arguably the most popular wireless data service for cellular networks. Due to its ubiquitous availability and universal support by mobile handsets and cellular carriers, it is also being considered for emergency notification and other mission-critical applications. Despite its increased popularity, the reliability of SMS service in real-world operational networks has received little study so far. In this work, we investigate the reliability of SMS by analyzing traces collected from a nationwide cellular network over a period of three weeks. Although the SMS service incorporates a number of reliability mechanisms such as delivery acknowledgement and multiple retries, our study shows that its reliability is not as good as we expected. For example the message delivery failure ratio is as high as 5.1% during normal operation conditions. We also analyze the performance of the service under stressful conditions, and in particular during a "flash-crowd" event that occurred in New Year's Eve of 2005. Two important factors that adversely affect reliability of SMS are also examined: bulk message delivery that may induce network-wide congestion, and the topological structure of the social network formed by SMS users, which may facilitate quick propagation of viruses or other malware.

/pdf/analysis-of-the-reliability-of-a-nationwide-short-message-3axek1cl60.pdf

Analysis of the Reliability of a Nationwide Short Message Service

Video transport over wireless networks requires retransmissions to successfully deliver video data to a receiver in case of packet loss, leading to increased delay time for the data to arrive at the receiver. Delay constraint is one of the most important requirements in real-time applications. A video packet arriving later than the presentation time will become useless for the client. In this paper, we propose a cross-layer content-aware retry limit adaptation scheme for video streaming over IEEE 802.11 wireless LANs. Video packets of different importance are unequally protected with different retry limits at the media access control (MAC) layer. The error propagation effect of each packet is estimated to guide the determination of its retry limit. More retry numbers are allocated to packets of higher loss impact to achieve unequal error protection. Our scheme also analyzes the backoff time for each retry and then takes into account the estimated backoff time for retransmission scheduling. Experimental results show that the proposed adaptation scheme can effectively mitigate the error propagation due to packet loss and assure the on-time arrival of packets for presentation, so as to improve video quality significantly.

/pdf/cross-layer-packet-retry-limit-adaptation-for-video-54ma1epnsb.pdf

Cross-Layer Packet Retry Limit Adaptation for Video Transport Over Wireless LANs

Device-to-device content caching techniques in 5G: A taxonomy, solutions, and challenges

A method for efficient short messages transmission in cellular networks is developed in this study. The number of short message service (SMS) messages is growing very rapidly, and existing cellular networks have to support a large number of SMS and signaling messages. The rate of SMS messages has already exceeded the rate of E-mail messages transmitted through the Internet, and their number keeps growing. SMS messages are characterized by a burst of a short, single packet message. Unfortunately, the protocols currently used by existing cellular networks cannot support this type of traffic efficiently. For this reason, SMS messages are currently transmitted through the signaling channel. Clearly, this usage of the signaling channel is far from being optimal, in terms of network resources utilization. Under certain conditions, it may even block the signaling channel. This study proposes to use a load-adaptive multiple access with congestion avoidance (LAMA/CA) for efficient short messages transmission in cellular networks. The LAMA/CA protocol is more stable, and much more efficient for transmitting SMS messages and signaling messages, than the existing method currently used in cellular networks. Moreover, the proposed method is superior to a collision-free protocol that uses a request to send (RTS) and clear to send (CTS) mechanism, over the range of packet lengths used for SMS messages and signaling messages.

An efficient short messages transmission in cellular networks

The issue of a multicast search for a group of users is discussed in this study. Given the condition that the search is over only after all the users in the group are found, this problem is called the Conference Call Search (CCS) problem. The goal is to design efficient CCS strategies under delay and bandwidth constraints. While the problem of tracking a single user has been addressed by many studies, to the best of our knowledge, this study is one of the first attempts to reduce the search cost for multiple users. Moreover, as oppose to the single user tracking, for which one can always reduce the expected search delay by increasing the expected search cost, for a multicast search the dependency between the delay and the search cost is more complicated, as demonstrated in this study. We identify the key factors affecting the search efficiency, and the dependency between them and the search delay. Our analysis shows that under tight bandwidth constraints, the CCS problem is NP-hard. We therefore propose a search method that is not optimal, but has a low computational complexity. In addition, the proposed strategy yields a low search delay as well as a low search cost. The performance of the proposed search strategy is superior to the implementation of an optimal single user search on a group of users.

Efficient multicast search under delay and bandwidth constraints

This study suggests to use popularity based caching for IP-based TV (IPTV) services over peer-to-peer (P2P) networks. Each peer in a P2P network can use two levels of cache hierarchy: an internal cache and a neighboring peer cache. Using this property, our main focus is on caching the globally most popular video files nearby the clients, in order to reduce the IPTV service delay, increase the quality of service provided to the clients, and reduce the traffic over the Internet backbone. The proposed framework was applied on real data traces from live P2P networks. The results demonstrate a significant improvement over the Least Recently Used (LRU) and the Least Frequently Used (LFU) cache management schemes. This study is motivated by the vision of large P2P networks consisting of many volunteers serving as peers, each of which has a relatively small cache size, in terms of the number of video items it can store. Since the performance of both the LRU and LFU schemes is very poor for small cache, there is a need for another cache management scheme, which outperforms these schemes, especially for small cache size. The proposed distributed popularity-based caching scheme can significantly increase the performance of P2P networks used for video streaming, with respect to the existing networks, that use the LRU or LFU schemes. The performance metric used for comparison is the cache hit ratio and the expected delay for content delivery. In both parameters a significant improvement is demonstrated.

Popularity-based caching for IPTV services over P2P networks

The issue of tracking a group of users is discussed in this study. Given the condition that the search is over only after all the users in the group are found, this problem is called the conference call search (CCS) problem. The goal is to design efficient CCS strategies under delay and bandwidth constraints. While the problem of tracking a single user has been addressed by many studies, to the best of our knowledge, this study is one of the first attempts to reduce the search cost for multiple users. Moreover, as oppose to the single user tracking, for which one can always reduce the expected search delay by increasing the expected search cost, for a multiple users search the dependency between the delay and the search cost is more complicated, as demonstrated in this study. We identify the key factors affecting the search efficiency, and the dependency between them and the search delay. Our analysis shows that under tight bandwidth constraints, the CCS problem is NP-hard. We therefore propose a search method that is not optimal, but has a low computational complexity. In addition, the proposed strategy yields a low search delay as well as a low search cost. The performance of the proposed search strategy is superior to the implementation of an optimal single user search on a group of users.

Establishing a mobile conference call under delay and bandwidth constraints

A method for efficient video streaming in wireless networks is developed in this study. The proposed method is especially suitable for beyond 3G (B3G) wireless networks. It offers a significant increase in the number of clients that the system can potentially serve simultaneously as well as a significant reduction in the expected waiting time for a service. Under high load conditions, the ratio of the expected waiting time for a service offered by the proposed method to the expected waiting time offered by the conventional method currently used for video streaming in wireless networks is very significant and increases exponentially with the load. Copyright © 2007 John Wiley & Sons, Ltd.

Zohar Naor

Papers

An efficient short messages transmission in cellular networks

Efficient multicast search under delay and bandwidth constraints

Popularity-based caching for IPTV services over P2P networks

Establishing a mobile conference call under delay and bandwidth constraints

Multicast video streaming for 4G wireless networks: Research Articles