In power control, convergence rate is one of the most important criteria that can determine the practical applicability of a given algorithm. The convergence rate of power control is especially important when propagation and traffic conditions are changing rapidly. To track these changes, the power control algorithm must converge quickly.
We study the effect of additional information on the convergence speed of CIR based power control algorithms. For that purpose we suggest two new algorithms and compare them with the distributed constrained power control (DCPC) algorithm. The first algorithm is called second-order power control (SOPC) algorithm [1,5] and the other is called block power control (BPC) algorithm [2,5]. SOPC utilizes power levels at current as well as previous iterations to compute power update in a distributed fashion. Gain for such a second-order algorithm is in faster convergence. In bunched systems, it is assumed that some of the link gains are available for radio resource management functions. BPC utilizes this partial knowledge of the link gain matrix to increase the convergence speed.
This work was done in co-operation with assistant professor Seong-Lyun Kim from the
Radio Communication Systems Group of Royal Institute of Technology, Sweden.
The distributed constrained power control (DCPC) is one of the most widely accepted algorithms by the academic community. It provides guidelines in designing power control algorithms for practical cellular systems and also constitutes a building block for other radio resource management algorithms. DCPC has a property that the power reaches the maximum level when a user is experiencing degradation of channel quality. Unfortunately, this high power consumption may not lead to sufficient improvement on channel quality and may even generate severe interference, hitting other users. This undesirable phenomenon happens more often when the system is congested. In this work (see [3] and [5]), we revisit and generalize DCPC in order not to necessarily use the maximum power when the channel quality is poor. We propose the concept of temporarily removing users with low channel quality. The generalized algorithm achieves better performance than DCPC in terms of power consumption and outage
This work was done in co-operation with Fredrik Berggren and assistant professor
Seong-Lyun Kim from the Radio Communication Systems Group of Royal Institute of
Technology, Sweden.
In wireless multimedia services, the system can provide a user with multiple data rates. The focus of this work is on the combined control of rates and powers for the system, in which a finite number of transmission rates are available. A selective power control (SPC) algorithm based on the generalized DCPC [3,5] has been suggested for this purpose. It has been pointed out that in the congested case SPC results in rapidly varying CIRs, which in turn can result in fluctuating transmission rates to users. At the same time, it will require frequent changes in the modulation and coding scheme to adapt to the CIR, which is undesirable in practice.
To reduce the rate switching frequency, we modify the SPC by adding an active link protection property to it. Furthermore, we show that the modified algorithm could be realized by utilizing only one bit for power control commands. Computational results indicate that the modified SPC achieves smaller outage probability with less rate changes while giving the same or slightly higher system throughput, compared with SPC. This work has been reported in [4] and [5].
This work was done in co-operation with assistant professor Seong-Lyun Kim from the Radio Communication Systems Group of Royal Institute of Technology, Sweden.