Method of controlling initial power ramp-up in CDMA systems by using short codes

• US 6,181,949 B1
• Filed: 01/06/1998
• Issued: 01/30/2001
• Est. Priority Date: 06/27/1996
• Status: Expired due to Term

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Lomp, Gary R., Ozluturk, Fatih M.
• Primary Examiner(s): Hunter, Daniel S.
• Assistant Examiner(s): Armstrong, Darnell R.
• Application Number:
  US09/003,104
• Time in Patent Office: 1,120 Days
• Field of Search: 455/510, 455/522, 455/67.1, 455/69, 455/437, 455/452, 455/67.4, 375/200
• US Class Current: 455/522
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/70753 Partial phase search
• CPC Class Codes: H04B 1/70755 Setting of lock conditions, e.g. threshold
• CPC Class Codes: H04B 1/70758 Multimode search, i.e. using multiple search strategies
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 1/708 Parallel implementation
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04B 2201/70703 using multiple or variable rates
• CPC Class Codes: H04B 2201/7071 with dynamic control of receiver resources
• CPC Class Codes: H04B 7/2628 using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] H04B7/2618 takes precedence
• CPC Class Codes: H04W 52/36 with a discrete range or set of values, e.g. step size, ramping or offsets
• CPC Class Codes: H04W 52/367 Power values between minimum and maximum limits, e.g. dynamic range
• CPC Class Codes: H04W 52/50 at the moment of starting communication in a multiple access environment
• CPC Class Codes: H04W 52/60 using different transmission rates for TPC commands

Abstract

A system and method of controlling transmission power during the establishment of a channel in a CDMA communication system utilize the transmission of a short code from a subscriber unit to a base station during initial power ramp-up. The short code is a sequence for detection by the base station which has a much shorter period than a conventional spreading code. The ramp-up starts from a power level that is guaranteed to be lower than the required power level for detection by the base station. The subscriber unit quickly increases transmission power while repeatedly transmitting the short code until the signal is detected by the base station. Once the base station detects the short code, it sends an indication to the subscriber unit to cease increasing transmission power. The use of short codes limits power overshoot and interference to other subscriber stations and permits the base station to quickly synchronize to the spreading code used by the subscriber unit.

Claims

1. A method for controlling transmission power during the establishment of communications between a base station and at least one subscriber unit, the method comprising:

transmitting a periodic signal from said subscriber unit at an initial predetermined power level;

increasing said power level at a predetermined ramp-up rate;

detecting said periodic signal at said base station when a sufficient power for detection is achieved;

transmitting a signal from said base station confirming that said periodic signal has been detected;

receiving said confirmation signal at said subscriber unit; and

ceasing the increase of the power level of the transmission of said periodic signal at said predetermined power level ramp-up rate when said confirmation signal is received.

2. The method of claim 1 wherein said initial predetermined power level is lower than the power level required for detection by said base station.

3. The method of claim 2 further including increasing the power level of said signal at a second predetermined rate, said second rate being less than said first rate.

4. The method of claim 3 wherein said first rate is approximately 1.0 dB/sec and said second rate is approximately 0.05 dB/sec.

5. A network for communicating between a base station and at least one subscriber unit, the network including a system for initial power control comprising:

said subscriber unit comprising;

means for selectively transmitting at least one access code at a selected transmission power level;

means for detecting a signal from said base station confirming the receipt of said access code; and

control means, responsive to said detecting means, for varying said transmission power level;

wherein said control means ceases increasing said transmission power level at a first rate upon the receipt of said confirmation signal and increases said transmission power level at a second rate after the receipt of said confirmation signal, said second rate being less than said first rate; and

said base station comprising;

means for detecting transmissions from at least one said subscriber unit, said transmissions including said access code; and

transmission means, responsive to said detecting means, for transmitting a confirmation signal to said subscriber unit when said access code is detected.

6. A communication network for conducting a plurality of concurrent communications using wireless transmissions between a primary station and at least one secondary station, the network including a power control system for controlling initial transmission power;

the power control system comprising;

the primary station having;

(i) means for transmitting a synchronization code;

(ii) means for detecting access codes transmitted from said at least one secondary station; and

(iii) means for generating a confirmation signal, said generating means being responsive to said detecting means; and

a first secondary station having;

(i) means for receiving the synchronization information from the primary station;

(ii) means for transmitting an access signal at a first transmission power level; and

(iii) means for increasing said transmission power level until said confirmation signal from said primary station is received whereupon the transmission of said synchronization code ceases.

7. A method for controlling transmission power ramp-up during establishment of communications between a base station and at least one subscriber unit, the method comprising:

transmitting from said subscriber unit a periodic signal at a predetermined power level, said power level being sufficiently low such that it will not be detected by said base station;

steadily increasing the power level of said signal at a predefined ramp-up rate;

detecting at said base station, the correct phase of said periodic signal when the signal achieves a sufficient power for detection by said base station;

transmitting, from said base station, a confirmation signal that said periodic signal has been detected;

receiving, at said subscriber unit, said confirmation signal, and;

ceasing the transmission of said periodic signal at the predetermined power level ramp-up rate at said subscriber unit when said confirmation signal is received.

8. The method of claim 7 further including increasing the power level of said signal at a second predefined ramp-up rate;

said second ramp-up rate being less than said first ramp-up rate.

9. The method of claim 8 wherein said first ramp-up rate is approximately 1.0 dB/sec and said second ramp-up rate is approximately 0.05 dB/sec.

10. A communication system for communicating between a base station and at least one subscriber unit, said communication system including a system for initial power control, said power control system comprising:

said subscriber unit comprising;

means for periodically transmitting a short access code having a predetermined length to said base station;

said short access code being transmitted at a first power level;

means for increasing said power level at a first power ramp-up rate;

means for detecting a transmission from said base station which confirms the receipt of said short access code at said base station; and

means, responsive to said detecting means, for ceasing increase of said power level at said first power ramp-up rate and periodically transmitting a long access code a second increasing power ramp-up rate;

said long access code having a predetermined length which is an even multiple of said short access code said second ramp-up rate being less than said first power increase rate; and

said base station comprising;

means for detecting transmissions from at least one said subscriber unit including said short and long access codes; and

transmission means, responsive to said detecting means, for transmitting a confirmation signal to said subscriber unit when said access codes are detected.