Virtual locating of a fixed subscriber unit to reduce re-acquisition time

• US 5,940,382 A
• Filed: 06/27/1996
• Issued: 08/17/1999
• 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: Haim, John W.
• Primary Examiner(s): TON, DANG T
• Application Number:
  US08/671,068
• Time in Patent Office: 1,146 Days
• Field of Search: 370/335, 370/310, 370/311, 370/312, 370/314, 370/320, 370/331, 370/332, 370/333, 370/337, 370/341, 370/345, 370/347, 370/351, 370/350, 370/318, 370/317, 370/319, 370/321 , 370/324, 370/342, 370/344, 370/343, 370/503, 370/441, 370/442, 370/479, 370/480, 370/519, 370/518, 370/517, 370/515, 370/512, 370/509, 370/505, 370/504, 370/506, 370/50 8, 455/56.1, 455/54.1, 455/54.2, 455/32.1, 455/33.4, 455/38.3, 455/67.6, 455/503
• US Class Current: 370/335
• 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 2201/70707 Efficiency-related aspects
• 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 52/362 Aspects of the step size
• 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 novel system and method reduces the time required by a base station to re-acquire a fixed subscriber unit in a CDMA communication system by virtually locating of the subscriber units. A base station acquires subscriber units by searching only those code phases concomitant with the largest propagation delay possible in the cell, as if all subscriber units were located at the periphery of the cell. A subscriber unit which has never been acquired by the base station varies the delay between the PN code phase of its received and transmitted signals over the range of possible delays in a cell and slowly ramps-up its transmission power until it is acquired by the base station. Upon initial acquisition by the base station, the subscriber unit ceases ramping-up its transmission power, ceases varying the delay and internally stores the final value of the delay in memory. For subsequent re-acquisition, the subscriber unit adds the delay value between the PN code phase of its received and transmitted signals, making the subscriber virtually appear to be at the periphery of the cell. This permits a quick ramp-up of transmission power by the subscriber unit and reduced acquisition time by the base station.

Claims

1. A method for reducing the reacquisition time of a subscriber unit by a base station in a network for communicating between a base station and at least one subscriber unit;

the method comprising;

transmitting an access signal from a subscriber unit at a predetermined power transmission level;

increasing said predetermined power transmission level until a confirmation signal is received from said base station;

detecting said access signal at said base station when a sufficient power level has been achieved;

transmitting a confirmation signal from said base station when said access signal has been detected;

receiving said confirmation signal at said subscriber unit;

ceasing the increase in transmission power from said subscriber unit when said confirmation signal is received;

calculating a delay value at said subscriber unit between said access signal and said confirmation signal; and

storing said delay for subsequent subscriber unit reacquisitions.

2. The method of claim 1 wherein said subscriber unit selectively increases said power level.

3. The method of claim 2 wherein the step of detecting at said base station further includes analyzing said access signal at a plurality of code phases.

4. The method of claim 3 further including generating a confirmation signal at said base station for transmission to said subscriber unit when a communication from the subscriber unit has been detected.

5. The method of claim 4 further including detecting, at said subscriber unit, a confirmation signal from said base station.

6. The method of claim 5 further including determining, at said base station, the duration between the transmission of a communication sent to said subscriber unit and the receipt of responding communication from said subscriber.

7. The method of claim 6 wherein said step of determining further includes calculating the difference between said determined duration and a desired duration.

8. The method of claim 7 further including transmitting, from said base station, a difference signal to said subscriber unit based upon said calculated difference.

9. The method of claim 8 further including receiving, at said subscriber unit, said difference signal and delaying signals transmitted from said subscriber unit by said difference.