AGC scheme and receiver for use in a wireless communication system
View Patent ↗Automatic gain control (AGC) and synchronisation acquisition by a communication unit in a wireless communication system, e.g. a Universal Mobile Telecommunication System (UMTS) system, is described. AGC is performed using a downlink beacon function, for example a power level (P beacon ) . Amplitude-equalising (limiting) is performed as part of synchronisation acquisition. Separate AGC processes are used for different stages of synchronisation acquisition. One AGC process uses a peak power (P(k)) of a received signal over a frame. Another AGC process uses a peak power (P(k)) of a received signal over only a portion of a frame, the portion comprising an initial synchronisation code. Another AGC process uses measurements of a received signal (P 0 (k)) taken in a downlink beacon timeslot. These processes tend to provide tolerance to a varying number of codes (M) transmitted on a timeslot-by-timeslot basis and robust initial synchronisation in the presence of strong uplink interference.
1. A method of performing automatic gain control (AGC) in a communication system, comprising:
measuring a total power (P t ) of signals received over a period of time;
determining a non-beacon serving cell power (P non-beacon );
determining a beacon power (P beacon );
computing an expected maximum power of transmissions to be received (P m ) using the total power (P t ), the non-beacon serving cell power (P non-beacon ), and a multiplier (M) of the beacon power (P beacon ); and
adjusting a receiver gain based at least on the computed P m .
2. A method of claim 1 , wherein computing the maximum expected power receipt (P m ) comprises computing:
P t -P non-beacon+(M− 1)* P beacon .
3. A method of claim 1 , wherein the multiplier (M) of the beacon power (P beacon ) is indicative of a maximum expected power received from a transmitter of the communication system during a period of time.
4. For a wireless communication system having a transmission format including a beacon timeslot and non-beacon timeslots, a method of synchronization acquisition using an automatic gain control (AGC), the method comprising:
clipping a high power signal received during at least one of the non-beacon timeslots without clipping a signal received in the beacon timeslot;
detecting a synchronization code position in a signal received during the beacon time slot;
setting a minimum allowable AGC gain (G min ) for application to received signals such that each received signal is sufficiently powerful to toggle at least a predetermined number of bits of an analog-to-digital converter (ADC) in spite of thermal noise in the receiver; and
applying an AGC gain over a frame period comprising the beacon timeslot and the non-beacon timeslots, wherein the AGC gain is at least the G min value; and
using the synchronization code position for identifying received data.
5. A method of claim 4 , wherein the predetermined number of bits is at least 4 bits.
6. A method of claim 4 , wherein a frame period comprises the beacon timeslot and the non-beacon timeslots, and clipping the high power signal comprises equalizing amplitudes and preserving phase information of received signals over the frame period.
7. A method of claim 4 , wherein clipping the high power signal comprises applying an analogue limiter.
8. A method of claim 4 , wherein clipping the high power signal comprises applying a digital limiter.
9. A computer readable medium storing program code for:
measuring a total power (P t ) of signals received over a period of time;
determining a non-beacon serving cell power (P non-beacon );
determining a beacon power (P beacon );
computing an expected maximum power of transmissions to be received (P m ) using the total power (P t ), the non-beacon serving cell power (P non-beacon ), and a multiplier of the beacon power (P beacon ); and
adjusting a receiver gain based at least on the computed P m .
10. The computer readable medium of claim 9 , wherein computing the maximum expected power receipt (P m ) comprises computing P t -P nonbeacon +(M−1)*P beacon .
11. The computer readable medium of claim 9 , wherein the multiplier of the beacon power is indicative of a maximum expected power received from a transmitter of the communication system during a period of time.
12. A computer readable medium storing program code for synchronization acquisition in a wireless communication system having a transmission format including a beacon timeslot and non-beacon timeslots, the program code for:
clipping a high power signal received during at least one of the non-beacon timeslots without clipping a signal received in the beacon timeslot;
detecting a synchronization code position in a signal received during the beacon time slot;
setting a minimum allowable AGC gain (G min ) for application to received signals such that each received signal is sufficiently powerful to toggle at least a predetermined number of bits of an analog-to-digital converter (ADC) in spite of thermal noise in the receiver; and
applying an AGC gain over a frame period comprising the beacon timeslot and the non-beacon timeslots, wherein the AGC gain is at least the G min value; and
using the synchronization code position for identifying received data.
13. The computer readable medium of claim 12 , wherein the predetermined number of bits is at least 4 bits.
14. The computer readable medium of claim 12 , wherein a frame period comprises the beacon timeslot and the non-beacon timeslots, and clipping the high power signal comprises equalizing amplitudes and preserving phase information of received signals over the frame period.
15. The computer readable medium of claim 12 , wherein clipping the high power signal comprises applying an analogue limiter.
16. The computer readable medium of claim 12 , wherein clipping the high power signal comprises applying a digital limiter.