Random access preamble detection for long term evolution wireless networks

1. A method of preamble detection in a random access channel of a wireless transmission system comprising the steps of:

receiving a transmitted signal;

converting the received signal into frequency-domain samples via a discrete Fourier transform;

demodulating a group of said frequency-domain samples to produce samples of the received signal;

converting said samples of demodulated signal into time-domain samples using an inverse fast Fourier transform;

modifying the time-domain samples to produce modified time-domain samples;

summing a group of modified time-time domain samples to produce a sum signal;

comparing the sum signal against a pre-computed preamble detection threshold calculated as follows

T

det

=

T

r

AN

nca

·

γ

n

where: T det and T r /AN nca are the respective absolute and relative preamble detection thresholds; A is the number of receive antennas: N nca is the number of non-coherent accumulations; and γ n is the noise floor estimate; and

detecting a preamble in the random access channel if the sum signal exceeds the pre-computed preamble detection threshold.

2. A method of preamble detection in a random access channel of a wireless transmission system comprising the steps of:

receiving a transmitted signal;

converting the received signal into a frequency domain samples via a discrete Fourier transform;

demodulating a group of said frequency-domain samples to produce samples of a demodulated signal by multiplying each frequency-domain sample by a complex number, each complex number being a complex-conjugate of a root preamble sequence selected from a set of all possible root preamble sequences;

converting said samples of demodulated signal into time-domain samples using an inverse fast Fourier transform;

modifying the time-domain samples to produce modified time-domain samples;

summing a group of modified time-time domain samples to produce a sum signal;

comparing the sum signal against a pre-computed preamble detection threshold;

detecting a preamble in the random access channel if the sum signal exceeds the pre-computed preamble detection threshold.

3. A method of preamble detection in a random access channel of a wireless transmission system comprising the step of:

receiving a transmitted signal;

converting the received signal into frequency domain samples via a discrete Fourier transform;

demodulating a group of said frequency-domain samples to produce samples of a demodulated signal;

converting said samples of demodulated signal into time-domain samples using an inverse fast Fourier transform;

modifying the time-domain samples to produce modified time-domain samples;

summing a group of modified time-time domain samples to produce a sum signal;

comparing the sum signal against a pre-computed preamble detection threshold;

detecting a preamble in the random access channel if the sum signal exceeds the pre-computed preamble detection threshold; and

calculating a channel quality information (CQI) by

detecting a channel impulse response (CIR) from the modified time-domain samples,

converting the detected channel impulse response into frequency-domain samples using an inverse fast Fourier transform, and

summing the frequency-domain samples over plural receive antennas.

4. The method of claim 3 , wherein:

said step of detecting a channel impulse response (CIR) employs a preamble detecting sliding window which contains a largest energy above a preamble detection threshold.

5. The method of claim 4 , wherein:

said step of detecting a channel impulse response (CIR) employs a timing advance (TA) estimate set to a highest peak delay within the sliding window which contains the largest energy above a preamble detection threshold.

6. The method of claim 4 , wherein:

said step of detecting a channel impulse response (CIR) employs a timing advance (TA) estimate set to the start of the sliding window which contains the largest energy above preamble detection threshold.

7. The method of claim 4 , wherein:

said step of calculating a channel quality information (CQI) further includes modifying time-domain samples by computing a square of a magnitude for each time-domain sample.

8. The method of claim 4 , wherein:

said step of calculating a channel quality information (CQI) further includes tail removal of said time-domain samples.

9. An apparatus for random access preamble detection in a wireless communication system, comprising:

a receiver antenna;

a discrete Fourier transform connected to the receiver antenna for converting a received signal into frequency-domain samples;

a plurality of root preamble frequency response units generating respective preamble frequency responses corresponding to all available root preamble sequences of user equipment seeking access;

a plurality of complex conjugation units, each connected to a corresponding one of said root preamble frequency response units, for forming a complex conjugate of a corresponding preamble frequency response;

a plurality of multipliers, each having a first input connected to said discrete Fourier transform, a second input connected to a corresponding complex conjugation units and a product output;

a plurality of inverse fast Fourier transforms, each connected to a corresponding multiplier for converting said products into time-domain samples;

a plurality of magnitude square units, each connected to a corresponding inverse fast Fourier transform forming a square of a magnitude for each time-domain sample;

a summer having inputs connected to each magnitude square unit for summing said square of a magnitudes; and

a comparator connected to said summer for comparing a sum signal from the summer with a preamble detection threshold and generating a detection signal if said sum signal exceeds said preamble detection threshold.

10. The apparatus of claim 9 , wherein:

said comparator includes a window filter.

11. The apparatus of claim 10 , wherein:

said window filter has a time-duration less than or equal to a time duration of a cyclic prefix (CP) of said received signal.

12. The apparatus of claim 9 , further comprising:

a channel quality information (CQI) unit including

a channel impulse response (CIR) unit connected to a corresponding inverse discrete Fourier transform for calculating a channel impulse response,

an inverse discrete Fourier transform connected to a corresponding channel impulse response converting the detected channel impulse response into time-domain samples, and

a summer connected to said inverse discrete Fourier transforms summing the time-domain samples thereby generating a channel quality information (CQI) signal.

13. The apparatus of claim 9 , wherein: said comparator includes

a noise floor estimator receiving a false alarm rate, a number of receive antennas, a number of non-coherent accumulations and the summed data from summer forming an estimate of a noise floor in received signals on plural channels,

a peak search unit receiving said sum signal and said noise estimate and setting said preamble detection threshold.