Wideband Code Division Multiple Access (WCDMA) telecommunication systems have many attractive properties that can be used for future development of telecommunication services. In particular, the enhanced uplink of the WCDMA system is one ingredient in the mobile broadband solution of WCDMA. Now, in order to retain stability of a WCDMA cell, possibly in a cell running enhanced uplink, the load needs to be kept below a certain level. This follows since the majority of uplink user channels, at least in WCDMA, are subject to power control. This power control aims at keeping the received power level of each channel at a certain signal to interference ratio (SIR), in order to be able to meet specific service requirements.
Since the Radio Base Station (RBS) tries to keep each channel at its specific preferred SIR value, it may happen that an additional user, or bursty data traffic of an existing user, raises the interference level, thereby momentarily reducing the SIR for the other users. The response of the RBS is to command a power increase to all other users, something that increases the interference even more. Normally this process remains stable below a certain load level. In case a high capacity channel would suddenly appear, the raise in the interference becomes large and the risk for instability, a so called power rush, increases. It is thus a necessity to schedule high capacity uplink channels, like the enhanced uplink (EUL) channel in WCDMA, so that one can insure that instability is avoided. In order to do so, the momentary load must be estimated in the RBS or any node connected thereto. This enables the assessment of the capacity margin that is left to the instability point.
To handle increasing uplink data rates, interference suppression (IS) and interference cancellation (IC) are being introduced in WCDMA. The main result is a reduction in the interference experienced by a user. The IS and IC also affect the load measurement functionality of the WCDMA enhanced uplink (EUL).
The instantaneous uplink load without IS/IC is today preferably obtained by a dedicated algorithm which estimates the rise over thermal (RoT), from measurements of the received total wideband power (RTWP) [1], [2]. There is also an uplink (UL) receiver structure concept defined that is a combination of the G-rake+ receiver and traditional interference cancellation (SIC) [3].
Prior art methods for estimating load without IC, RoT estimation algorithms without IS/IC and IC methods with regeneration and subtraction are discussed more in detail in Appendix A.
There are a number of IS/IC methods available in prior art. Frequency domain equalization (FDE) and Frequency domain pre-equalization (FDPE) are two examples, where the interference is handled in the frequency domain, i.e. they are frequency domain receiver techniques.
Minimum mean square error (MMSE) FDE is a common technique to combat frequency selectivity in wideband channels, like in the WCDMA uplink. FDE can be seen as providing a counterpart to the G-rake receiver. The main advantages, as compared to time domain equalization, include a reduced complexity. FDE primarily provides (self-)interference suppression
FDPE is another frequency domain technique for interference suppression that has been developed as an alternative to the G-rake+ receiver structure. The main advantages associated with FDPE as compared to G-rake+ are claimed to be a lower complexity, a simpler receiver structure where much can be reduced and algorithms that may re-use LTE ASIC accelerators for fast Fourier transforms. At the same time, most of the interference suppression gains associated with the G-rake+ receiver remain.
An overview of these techniques is given in Appendix B.
The prior art cell stability load estimation functionality, exploits load factors for each user. In their simplest form the load factors are given by:
            L      u        =                            P          u                RTWP            =                                    (                          C              /              I                        )                    u                          1          +                                    (                              C                /                I                            )                        u                                ,      u    =    1    ,  …  ⁢          ,  U  ,where Pu is the power of user u. Load factors are then summed up, for each power controlled user. In this way the neighbor cell interference is not included in the resulting load measure. This is reasonable since the neighbor cell interference should not affect the own cell power control loop, at least not when first order effects are considered.
However, using prior art solutions of [1], [2] for load estimation, the scheduler will experience the load before IS or IC, e.g. according to FDE or FDPE, is applied. Hence the scheduling performance will then be the same as without IS or IC, i.e. under-scheduling and under-utilization will result.
A problem with existing load estimation algorithms compatible with the FDE and FDPE receiver structures, known in public prior art, is that they overestimate the air-interface load of the uplink, relevant for cell stability. Thereby they cause under-scheduling in the RBS, which results in a too low throughput and/or capacity. They also cause blocking in the admission control function in the RNC, which also results in reduced throughput/capacity. Another problem is also that the admission and congestion control algorithms that reside in the RNC are not able to admit users so that the uplink with IS/IC is fully exploited.