Fredrik Berggren

N-continuous OFDM

In this letter we report a new OFDM signalling format characterized by a precoder that renders the emitted signals phase and amplitude continuous. It achieves superior out-of- band power characteristics at the price of a slightly reduced receiver sensitivity.

Asymptotically fair transmission scheduling over fading channels

The problem of scheduling delay insensitive data over a direct sequence code-division multiple-access downlink fading channel is considered. This work considers the case where only one user at a time is allowed to transmit. As the channels can be considered to vary asynchronously among the users, multiuser diversity gains can be obtained by exploiting channel adaptive scheduling. For this, schedulers of different adaptation rate are suggested and compared. In particular, the authors analyze a simple fast scheduler that schedules a user to transmit when its channel is good relative to its mean. This scheduler is resource fair in the sense it can provide the users with the same asymptotic channel access. They show that the achievable scheduling gain compared to round robin is equal to the gain of a selection diversity scheme. The scheduling gain is determined, both on closed-form and by numerical integration, for several scenarios, including multicellular systems and the effect of time delayed channel estimates. The results show that the scheduling gain is larger for channels with low average quality.

Joint power control and intracell scheduling of DS-CDMA nonreal time data

The performance of DS-CDMA systems depends on the success in managing interference arising from both intercell and intracell transmissions. Interference management in terms of power control for real time data services like voice has been widely studied and shown to be a crucial component for the functionality of such systems. In this work we consider the problem of supporting downlink nonreal time data services, where in addition to power control, there is also the possibility of controlling the interference by means of transmission scheduling. One such decentralized schedule is to use time division so that users transmit in a one-by-one fashion within each cell. We show that this has merits in terms of saving energy and increasing system capacity. We combine this form of intracell scheduling with a suggested distributed power control algorithm for the intercell interference management. We address its rate of convergence and show that the algorithm converges to a power allocation that supports the nonreal time data users, using the minimum required power while meeting requirements on average data rate. Numerical results indicate a big potential of increased capacity and that a significant amount of energy can be saved with the proposed transmission scheme.

A generalized algorithm for constrained power control with capability of temporary removal

The distributed constrained power control algorithm (DCPC) (Grandhi et al. 1995) has become one of the most widely accepted quality-based power control algorithms by the academic community. The DCPC has a property that the power may reach the maximum level when a user is experiencing degradation of channel quality. Unfortunately, using maximum transmitter power may not lead to sufficient improvement of channel quality and will thereto generate severe interference, affecting other users. This undesirable phenomenon happens more often when the system is congested. In this paper, we revisit and generalize the DCPC algorithm in order not to necessarily utilize the maximum power when the channel quality is poor. Under poor quality conditions, rather than combating the interference by maximizing power, we propose the concept of reducing the powers and temporarily removing users from the channel. We show that the energy consumption can be reduced through our generalized algorithm and we prove its convergence properties. Because of the decreased interference power, the capacity of the system is expected to increase. To validate this, we made computational experiments suggesting that the proposed algorithm can support more users in a congested system as compared to the previously suggested distributed removal algorithm gradual removals restricted (GRR)-DCPC (Andersin et al. 1996).

Energy-efficient control of rate and power in DS-CDMA systems

The quality of service in direct-sequence code-division multiple access (DS-CDMA) can be controlled by a suitable selection of processing gain and transmission powers. In this paper, distributed control of rate and power for best effort data services is considered. In particular, we elaborate on the problem of how to control the transmission rates for maximizing system throughput while simultaneously minimizing the transmission powers. We assume a practical scenario, where every user has a finite set of discrete transmission rates and propose a simple heuristic rate allocation scheme, greedy rate packing (GRP), applicable in both up- and downlink. The scheme can be interpreted as a practical form of water-filling, in the sense that high transmission rates are allocated to users having high link gains and low interference. We show that under certain conditions, GRP will give maximum throughput and that it can be extended to guarantee a minimum data rate while maximizing network excess capacity. We suggest and analyze a distributed power control algorithm to control the intercell interference when GRP is applied to a multicellular system. Numerical results show that the proposed transmission scheme can significantly decrease the power levels while maintaining high throughput.

Out-of-Band Power Suppression in OFDM

In this letter we show that judicious modulation of non-data subcarriers renders a transmitted OFDM signal and a few of its higher-order derivatives continuous at the OFDM symbol boundaries. This novel approach results in reduced out-of-band emission: typically, it achieves over 30 dB power suppression at adjacent-channel center-frequencies.

A simple bound on the outage probability with lognormally distributed interferers

We consider the problem of determining the outage probability in a cellular radio system, where the interference is modeled by a sum of lognormal random variables. As no closed form expression is known, bounds can serve as a quick way of evaluating performance. By applying the arithmetic-geometric mean inequality, we give a lower bound, computationally simple as it is expressed by a single Q-function. The bound includes the case of correlated interferers and background noise. Numerical evaluation for a range of parameters valid for practical applications, shows good accuracy for moderate variances and improvement over a previously suggested bound. This is especially emphasized when the number of interferers is large.

Primary Synchronization Signal in E-UTRA

In this paper, we describe the signal design for primary synchronization channel adopted for E-UTRA cellular system. By designing the signal to be centrally symmetric in the time-domain, the symmetric samples can be added prior to multiplication with the replica sample, thereby saving one multiplication per two received samples. Furthermore, a pair of centrally symmetric P-SCH signals can be generated such that one signal is a complex conjugated version of the other signal. The multiplication complexity of detecting both these signals can be reduced to that of just one of the signals.

Multi-radio resource management for communication networks beyond 3G

In ‘Beyond 3G’ wireless networking scenarios, characterized by the cooperation of multiple access networks comprising different radio access technologies, Multi-Radio Resource Management (MRRM) mec ...

Multiuser scheduling over Rayleigh fading channels

Forthcoming wideband wireless systems are supposed to support services with loose delay requirements, which allows for scheduling of data. In this work we investigate fast transmission scheduling for downlink CDMA over a Rayleigh fading channel. For a logarithmic relation between the channel quality and the effective transmission rate, merely scheduling one user at a time may not result in maximum channel utilization. Therefore, we analyze the benefits of scheduling several users at a time with a suggested scheduler, containing regular CDMA as a special case. We consider a resource fair scheduler with the objective to asymptotically allocate the same amount of energy to all users. We derive the scheduling gain on closed-form and determine its limit values for both high and low average channel quality. The results show that the better the average channel quality becomes, the more users should be allowed to transmit simultaneously.