Method of estimating BER values in a wireless communication system
There is provided a method of estimating a bit error rate in a transport channel of a wireless communication system. The method comprises the receiving a signal from a remote transmitter of the wireless communication system via a physical channel, the signal comprising data and noise forming a plurality of soft bits. The method further comprises the counting, during a period of time, a number of erroneous bits being those soft bits which have an amplitude below −2A or above +2A with A being the average amplitude of the soft bits received. Next, the number of erroneous bits is divided by a number of total bits received during said period of time in order to obtain the bit error rate. This method provides a way to estimate the BER value without knowing the exact shape of the noise distribution. In an embodiment a selection is made between two estimation algorithms.
1. A method of estimating a bit error rate in a transport channel (TrCH) of a wireless communication system, the method comprising:
receiving a signal from a remote transmitter of said wireless communication system via a physical channel (PhCh), said signal comprising data and noise forming a plurality of soft bits;
selecting between a first estimation method and a second estimation method depending at least one channel parameter, the first estimation method comprising:
counting, during a period of time, a number of erroneous bits being those soft bits out of said plurality which have an amplitude below −2A or above +2A with A being an average amplitude of the soft bits received; and
dividing the number of erroneous bits by a number of total bits received via said transport channel during said period of time in order to obtain the bit error rate; and
the second estimation method comprising:
determining a noise power estimate of the soft bits received;
determining a Signal to Noise Ratio (SNR) estimation value using said noise power estimate;
improving the SNR estimation value by removing a systematic error which was introduced during the SNR estimation determination, to render an improved SNR estimation value; and
converting the improved SNR estimation value to a bit error rate value based on an analytical relation between the improved SNR estimation value and the bit error rate.
2. A method according to claim 1 , wherein said period of time is a time transmission interval (TTI) of said transport channel (TrCH).
3. A method according to claim 1 , wherein said second estimation method comprises:
calculating a Signal to Noise Ratio (SNR) estimation value using the formula:
SNRest
=
P
signal
P
noise
≅
A
2
1
N
∑
i
=
1
N
noise
(
i
)
2
=
NA
2
∑
i
=
1
N
noise
(
i
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2
with
Psignal a power of the signal, Pnoise the power of the noise
N a number of samples used in the estimation
A an average signal amplitude
noise(i) an ith sample of noise.
4. A method according to claim 1 , wherein said at least one channel parameter is a spreading factor (SF) of said physical channel (PhCH).
5. A method according to claim 4 , wherein the first estimation method is selected if said spreading factor is smaller than a predefined value.
6. A method according to claim 5 , wherein said predetermined value is 32.
7. A method according to claim 1 , wherein said at least one channel parameter comprises a transport channel size and a repetition factor of said transport channel.
8. A method according to claim 7 , wherein said selection is made depending on whether said transport channel size is smaller than a function of the repetition factor.
9. A method according to claim 1 , wherein said selecting comprises accessing a lookup table with as input parameters a repetition factor value and a transport channel size value, to render an output parameter indicating whether the first estimation method or the second estimation method is to be used.
10. A method according to claim 1 , wherein said transport channel is an entity of the UMTS(WCDMA) standard.
11. A network node of a wireless communication network, said network node comprising:
a receiver for receiving a signal from a remote transmitter of said wireless communication system via a physical channel (PhCH), said signal comprising data and noise forming a plurality of soft bits;
a selection circuit for selecting between a first bit error rate (BER) estimation of a transport channel and a second BER estimation of the transport channel depending at least one channel parameter;
the first BER estimation uses a counter and a divider,
the counter for counting, during a period of time, a number of erroneous bits being those soft bits out of said plurality which have an amplitude below−2A or above +2A with A being the average amplitude of the soft bits received; and
the divider for dividing the number of erroneous bits by a number of total bits received via said transport channel during said period of time in order to obtain the bit error rate; and
the noise power estimation of the received soft bits is determined;
the SNR estimation is determined using the noise power estimation;
the SNR estimation is improved by removing a systematic error which was introduced during determination of the SNR estimation; and
the improved SNR estimation is converted to the BER based on an analytical relation between the improved SNR estimation and the BER.
12. A mobile communication device, the device comprising:
a receiver for receiving a signal from a remote transmitter of said wireless communication system via a physical channel (PhCH), said signal comprising data and noise forming a plurality of soft bits;
a selection circuit for selecting between a first bit error rate (BER) estimation of a transport channel and a second BER estimation of the transport channel depending at least one channel parameter;
the first BER estimation uses a counter and a divider,
the counter for counting, during a period of time, a number of erroneous bits being those soft bits out of said plurality which have an amplitude below −2A or above +2A with A being the average amplitude of the soft bits received via said physical channel (PhCH); and
the divider for dividing the number of erroneous bits by a number of total bits received via said physical channel, during said period of time in order to obtain the bit error rate; and
the second BER estimation uses a noise power estimation and a signal to noise ratio (SNR) estimation,
the noise power estimation of the received soft bits is determined;
the SNR estimation is determined using the noise power estimation;
the SNR estimation is improved by removing a systematic error which was introduced during determination of the SNR estimation; and
the improved SNR estimation is converted to the BER based on an analytical relation between the improved SNR estimation and the BER.
13. A computer program product comprising instructions for causing a processor system to perform a method according to claim 1 .