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Wireless IP

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Error free transmission is not always possible in todays nor future's communication networks without making retransmissions. Retransmissions, however, introduce delay. To delay sensitive applications the concept of soft information, i.e. lower layer knowledge about the channel conditions, could reduce the number of retransmissions. This paper explores the utilization of soft information in image decoding. It is not sufficient to treat the soft information and the image decoder separately. By combining soft information and error resilience in the decoder the image quality can be improved. Two modified JPEG2000 image decoders that utilize soft information have been developed. Experiment results with images transmitted over a simulated wireless channel show that a simple decoding process which utilizes soft information can give high gains in image quality. Only marginally higher gains are observed with a more complex decoding process

This paper proposes that fairness in wireless networks should be measured using one of the following new measures: the deterministic unfairness bound called the wireless absolute fairness bound (WAFB) or the statistical unfairness bound called the 99-percentile wireless absolute fairness bound (WAFB99). Compared with previous fairness de_nitions, the new fairness measures are better suited for measuring fairness of scheduling disciplines that exploit multiuser diversity. A new scheduling discipline called opportunistic proportional fair scheduling is de_ned. Numerical results show that the new scheduling discipline has slightly higher throughput and slightly better fairness than proportional fair scheduling.

In this paper we describe an OFDM based 4G downlink for a wide area coverage and high mobility system. User data are multiplexed and OFDM modulated such that the user with the best predicted channel conditions are always using the channel. This user employs the linear modulation scheme that maximizes the spectral efficiency. We show that the system obtains a sector capacity that is significantly better than current 3G systems. Various combinations of OFDM and CDMA are also discussed and it is concluded that it is difficult to motivate the significantly increased complexity of such schemes. Moreover, we also doubt that these combinations can increase spectral efficiency when predicted channel information is utilized at the transmitter

A packet switched wireless cellular system with wide area coverage, high throughput and high spectral efficiency is proposed. Smart antennas at both base stations and mobiles improve the antenna gain and improve the signal to interference ratio. The small-scale fading is predicted in both time and frequency and a slotted OFDM radio interface is used, in which time-frequency bins are allocated adaptively to different mobile users, based on their predicted channel quality. This enables efficient scheduling among sectors and users as well as fast adaptive modulation and power control. We here estimate the spectral efficiency of the suggested downlink. The resulting channel capacity grows with the number of simultaneous users and with the number of antenna elements in terminals. A high efficiency, around 4 bits/s/Hz, is attained already for moderate numbers of users and terminal antennas. An outline is given of research pursued within the PCC Wireless IP Project to improve and investigate this type of system.

A packet switched wireless cellular system with wide area coverage and high throughput is proposed. It is designed to be cost effective and to provide high spectral efficiency. The high performance is achieved by the use of long term channel predictions, in both time and frequency, scheduling among users, and smart antennas combined with adaptive modulation and power control. Calculations of the spectral efficiency of the downlink, based on reasonable simplifying assumptions, indicate that a tremendous capacity can be attained for moderate numbers of users and terminal antennas. We also briefly discuss other means for performance improvements such as alternatives to standard TCP, interlayer interaction/communication, and the use of positioning information.

The underlying physical link is transparent in most IP-based networks. Contrary to this commonly accepted design rule, we propose that the applications should be made aware of the channel conditions. This is especially fruitful for wireless links where the performance is many orders of magnitudes lower than in fixed networks. Instead of wasting resources to make the wireless link behave as a fixed link, the application could take care of the adaptation to the channel condition. The presented solution assumes that soft information consisting of a reliability measure of the received bits is produced in the physical layer. This soft information is then propagated to the application. The application may use this information to distinguish between errors caused by fading and network congestion. Another possible use for soft information is to make the applications adapt the source and channel codes to the current channel condition and thus maximize performance.