WO2001054289A2

WO2001054289A2 - Method for determining the current signal-to-interference ratio and for controlling the power in mobile radio systems comprising code division multiplex

Info

Publication number: WO2001054289A2
Application number: PCT/DE2001/000239
Authority: WO
Inventors: Markus Doetsch; Peter Jung; Tideya Kella; Jörg PLECHINGER; Peter Schmidt; Michael Schneider
Original assignee: Infineon Technologies Ag
Priority date: 2000-01-20
Filing date: 2001-01-19
Publication date: 2001-07-26
Also published as: DE10002327A1; WO2001054289A3

Abstract

The invention relates to a method for determining the current signal-to-interference ratio and for controlling the power in mobile radio systems comprising code division multiplex. According to said method, sequences of known symbols are transmitted between unknown data symbols from a base station. The determination of the current signal-to-interference ratio takes place by comparing the known symbols with the corresponding received data which has been altered by interference and channel fading.

Description

description

Method for determining the current signal-to-noise ratio and for power control in mobile radio systems with code division multiplex

The present invention relates to a method for determining the current signal-to-noise ratio and for power control in mobile radio systems with code division multiplex, in which sequences of known symbols are transmitted by a base station between unknown data symbols.

In ideband CDMA systems, fast power control is required to maintain system performance. Unregulated performance of individual participants can possibly lead to the supply of all participants in a system being prevented. In order to enable reliable power control, the base station sends the known signals to the mobile subscribers, which signals are used by them to measure the power. With the help of these measurements, the mobile subscribers gain knowledge of the current signal-to-noise ratio (SNR). This knowledge is used by the mobile subscribers to send power control commands to the base station. It is clear that accurate measurement of performance is essential for optimized system performance.

State of the art in today's systems with CDMA (ANSI-95) is the estimation of the SNR solely on the basis of continuously transmitted pilot signals. Since the received signal contains both unknown components, in the form of noise and channel fading, and also known components, namely the pilot signals known to the receiver, an estimate of the SNR can be determined using the known components. This state of the art for power regulation results, for example, from the book "CDMA" by Andrew J. Viterbi from the Addisonley ireless Communications Series, pages 116 to 119. According to this state of the art, the power control was always based on the reception quality of the common pilot channel. However, this is always transmitted by the base stations with a constant strength, while the dedicated channels on which the data are sent for the individual mobile radio receivers are broadcast with different powers. A power control based on the common pilot channel, as shown in the prior art, is therefore not optimal.

It is therefore an object of the present invention to provide an improved method for determining the current signal-to-noise ratio and for power control in mobile radio systems with code division multiplex, in particular for mobile radio systems according to the new UMTS standard.

According to the invention, this object is achieved by such a method in which the current signal-to-noise ratio is determined by comparing the known symbols with the corresponding received data changed by noise and channel fading.

It is particularly preferred if, in addition to the known symbols (pilot symbols), adjacent data symbols are also used to determine the current signal-to-noise ratio.

It is particularly preferred to decorrelate the received signal for the real and imaginary parts separately with the scrambling code and the channelization code for each RAKE finger, so that a decorrelated signal is present in the code element clock for each finger, and the signals for Real and imaginary parts are despread separately, so that a signal to be processed is present separately in the symbol cycle for real and imaginary parts, and then real and imaginary parts can be combined so as to obtain the received data used to determine the signal-to-noise ratio.

If, in accordance with the UMTS standard, the base station additionally sends a sequence of known symbols on a common channel (common pilot channel) for all participants in continuous operation, the determination of the signal-to-noise ratio between the transmissions of the known symbols can be based on The change in the signal-to-noise ratio determined on the basis of the continuous operation on the common channel is tracked in order to be able to compensate for fluctuations in the transmission quality between the individual transmissions of known sequences.

The present invention further teaches a method for power control in code division multiplexed mobile radio systems, wherein the signal-to-noise ratio determined according to the methods described above is used to calculate corresponding power control commands that are sent to the base station and there the transmission power of the base station is regulated accordingly.

The present invention is explained in more detail below with reference to the embodiment shown in the drawings. It shows:

1 shows the data structure of the individual RAKE fingers for the real and imaginary part; and

2 shows the carrier power estimate for the complex signals.

In the following, the power control according to the invention is first to be shown in the reception path.

The power control is based on a power control with a closed control loop, which the transmission power of the mobile Station so that the signal-to-interference ratio (SIR) for the signal received in the base station is kept at a predetermined SIR setpoint. For this purpose, the mobile station estimates the received power of the dedicated physical channel (DPCH) in the downward direction by combining the maximum ratios (maximum ratio combining = MRC). At the same time, the mobile station estimates the total interference received in the downlink direction in the current frequency band. The commands for controlling the transmission power of the base station (transmission power control = TPC) are generated on the basis of these measurements.

All of the above Processing steps can be performed by firmware in a signal processor.

The signal level is estimated based on the instantaneous energy of the pilot symbols according to maximum ratio combining (MRC). This can also be done by firmware in a signal processor.

The signal level estimate is calculated using the following formula:

S = - £ ⁽ p _k ^{r) 2} + ⁽ p _k ^{X) 2} ^N pilot k = 0

where Npüot represents the number of pilot symbols used for energy estimation and p _{k represents} the received pilot symbols. The indices r and i denote the real or imaginary part of the corresponding size.

The level of interference is estimated based on the fluctuation in the energy of the pilot bits using maximum ratio combining (MRC).

The interference level is calculated as follows: σ _n ² = variance ^ i), i = 0 ... N _pilot - 1,

where Si represents the estimated energy of the pilot symbols and n denotes the slot index.

The variance is filtered with a first-order IIR filter (Infinite impulse response filter = filter with unlimited impulse response) as follows:

The signal-to-noise ratio estimated for a slot then corresponds to:

S

SIRest y ^'

This means that the variance used in the current slot for SIR estimation is made up of the currently calculated variance and a variance filtered in the previous slots.

The commands for controlling the transmission power (TPC commands) are generated according to the following rules:

SIR _est > SIR _target - »TPC = down SIR _est <SIR _target → TPC = up.

The value of SIR _ta rget is set by the network depending on the quality of service. The corresponding control commands for the transmission power are transmitted with the next time slot. In the transmission direction of the mobile station, the transmission power is regulated as follows:

After a transmit power control command (TPC command) has been generated, the transmit power of both the upward dedicated physical control channel (DPCCH) and the upward dedicated physical data channel (DPDCH) is in the specified one Direction set with a step size of Δ _TPC . The step size Δ _TPC is a parameter that is cell-specific and should be between 0.25 and 1.5 dB.

In the case of a "soft hand over", the control commands from different base stations are compared and the transmission power is only increased if all base stations give a corresponding command to increase the transmission power.

If one of the commands of the different base stations requests a reduction in the transmission power, the transmission power is reduced by a corresponding step size Δ _TPC . If more than one command to reduce the transmission power is received, the command with the largest increment is selected and the transmission power is reduced by this largest increment.

The mathematical foundations for determining the signal-to-noise ratio (SNR) according to the present invention are explained in more detail below:

As is common with code division multiplex signals in mobile radio traffic, the received signal is processed slot by slot in a RAKE receiver. The following reception signal results:

The received signal is decorrelated with the scrambling code and the channelization code for each finger, so that a decorrelated signal is present in the chip clock for each finger. The decorrelation is carried out separately for the real and imaginary parts.

It applies to the real part:

^r rea -1l ⁼ ( ^r real; l ' ^r real 2''"* ^r real; N''D = lr ^{• • •} > K

with r _{real; i + delay []} - C_ ^■ ^ reaiii + άela.ylj] and rj _{eal; i} = 0 Vi <delayfj]

where K is the number of RAKE fingers used. Ci is the code sequence that belongs to the current slot and designates the product of the scrambling and channelization code.

The data structure for both the real and the imaginary part is shown in FIG. 1.

The signals for the real and imaginary parts are now despreaded so that the signal to be processed is available in symbol cycle:

^ real ⁼ ^ real; l ^d real; 2 ' ^{• • • C} ^ real; N _sym b-slot ^ ^m "'" ^t

^d real; i = ^SF = spreading factor

For each finger j there is now a signal in the symbol cycle for I (= in-phase) and Q (= quadrature) channel. Real and imaginary parts are combined and offset for channel estimation.

^- d ^j = (~ dj, d ~ \ ^Δ ... _ ^W symb-slot)

The channel estimation is carried out with the known pilot symbols s _p ii _ot i as follows:

The symbols are then weighted and combined:

§ ⁼ ^ -Npilot + 1 '§Npilot + 2''-§N'

K with li = ∑ di ^j - (chV; i> N _pilot

Now the performance can be estimated:

The carrier power estimate is carried out with output values from the combiner projected onto the real axis:

1 - j; Rejs> 0.1 ^}> 0

1 + j; Rejs> 0, I _mi } <0 with hard (s) = ^~ - 1 + j; Rejf <0.1 ^} <0

- 1 - j; Rejs <0, I _m {s _i }> 0

The first term in the formula for c _es t uses the known pilot symbols; N _m denotes the total number of symbols used for the carrier power estimation, ie Npüo pilot symbols and (N _m -N _P ii _ot ) data symbols are used.

Assumption is:

s _L = ch ^* - (ch • s _i + n) if n - »0

(ipiiot ⁾ = l ^ch n where (Spiiot) has a square of magnitude of 1, ch denotes the summed contribution of the channel weights of the individual transmission paths, which are resolved with the RAKE fingers, and n denotes the summed noise contribution from all RAKE fingers.

The second term rotates the outputs from the combiner towards the real axis:

This is shown in Fig. 2.

The real part of both expressions added up, normalized to the number of symbols used for the calculation, results in the received carrier power. So data symbols are also used for the carrier power estimation - and thus also for the determination of the SNR.

The interference estimation is only carried out using the pilot symbols:

^S piiot

I = h ^■ fcpiiotii / ¹ -∑ feh ^j

N. pilot i = ι: = ι

Claims

claims

1. Method for determining the current signal-to-noise ratio in mobile radio systems with code division multiplex, in which sequences of known symbols are sent from a base station between unknown data symbols, characterized in that the determination of the current signal-to-noise Ratio by comparing the known symbols with the corresponding received data changed by noise and channel fading.

2. The method according to claim 1, so that in addition to the known symbols, adjacent data symbols are also used to determine the current signal-to-noise ratio in addition to the known symbols.

3. The method according to claim 1 or 2, dadurchg ek indicates that the received signal for real and imaginary part is decorrelated separately with the scrambling code and the channelization code for each RAKE finger, so that a decorrelated signal for each finger is present in the chip clock and the signals are then despread separately for real and imaginary parts, so that a signal to be processed is present separately in the symbol clock for real and imaginary parts, and then real and imaginary parts are combined so as to determine the signal -to-noise ratio received data can be obtained.

4. The method according to any one of claims 1 to 3, wherein the base station additionally sends a sequence of known symbols on a common channel (common pilot channel) for all participants in continuous operation, characterized in that the determination of the signal-to-noise Relationship between the broadcasts of the known symbols based on the change in the signal-to-noise ratio determined on the basis of the continuous operation on the common channel.

5. A method for power control in mobile radio systems with code division multiplex, characterized in that the signal-to-noise ratio determined according to one of claims 1 to 4 is used to calculate corresponding power control commands that are sent to the base station, and there the transmission power the base station is regulated accordingly.