Cellular mobile telephone system

• US 6,178,194 B1
• Filed: 01/14/1998
• Issued: 01/23/2001
• Est. Priority Date: 01/16/1997
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Vasic, Dobzica
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Ghayour, Mohammad
• Application Number:
  US09/006,843
• Time in Patent Office: 1,105 Days
• Field of Search: 375/136, 375/137, 375/147, 375/148, 375/326, 375/341, 375/342, 375/343, 375/316, 455/63, 455/226.1, 455/516, 455/517
• US Class Current: 375/136
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 2027/0046 Open loops
• CPC Class Codes: H04L 2027/0095 in a preamble or similar structure
• CPC Class Codes: H04L 27/2332 using a non-coherent carrier
• CPC Class Codes: H04W 52/08 Closed loop power control
• CPC Class Codes: H04W 52/12 Outer and inner loops
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

A cellular mobile telephone system includes a first carrier estimation stage that estimates carrier signals using pilot symbols that have been inserted a signal received by the telephone system. The pilot symbols have a known code pattern. The first carrier estimation stage produces a data symbol train. A second carrier estimation stage estimates the carrier signals using the data symbol train and the pilot symbols. In this way, the telephone system can reproduce a highly precise carrier used in coherent detection in a cellular mobile CDMA system.

Claims

1. A cellular mobile telephone system comprising at least one cell device and at least one mobile device which mutually transmit and receive an information signal, said cell device being provided with a channel estimation circuit which estimates carriers of receiving signals received from said at least one mobile device, each channel estimation circuit comprising:

a first estimation circuit which performs a first stage carrier estimation using pilot symbols having a known pattern, said pilot symbols being disposed in a corresponding receiving signal, said first estimation circuit thereby producing first stage estimated carrier signals;

a pre-detection circuit which receives said first stage estimated carrier signals and produces a data symbol train corresponding to said corresponding receiving signal in response thereto; and

a second estimation circuit which receives said data symbol train and said pilot symbols and performs a second carrier estimation with respect to said corresponding receiving signal, said second estimation circuit producing second stage estimated carrier signals as a result.

2. A cellular mobile telephone system as claimed in claim 1,

wherein said cell device further comprises a diversity combiner circuit which coherently combines said corresponding receiving signal with said second stage estimated carrier signals.

3. A cellular mobile telephone system as claimed in claim 1,

wherein each channel estimation circuit further comprises:

an Eb/Io calculator, said Eb/Io calculator receives said second stage estimated carrier signals and said pilot symbols and produces an Eb/Io output in response thereto; and

a power controller which receives said Eb/Io output and generates a power adjustment command corresponding to a deviation between said Eb/Io output and a threshold Eb/Io output.

4. A cellular mobile telephone system as claimed in claim 3, wherein said mobile device comprises another power control which receives said power adjustment command and regulates a power of a transmission signal produced by said mobile device in response to said power adjustment command.

5. A cellular mobile telephone system as claimed in claim 1, wherein said information signal is transmitted and received by using a code division multiple access (CDMA) spread spectrum communication signal.

6. A cellular mobile telephone system as claimed in claim 1, wherein:

one of said first estimation circuits and one of said second estimation circuits is provided for each communication path of a channel of said corresponding receiving signal; and

said pre-detection circuit includes a phase and amplitude adjustment circuit which adjusts the amplitude and phase of said first stage estimated carrier signals thereby producing adjusted signals a diversity combining circuit which coherently combines said adjusted signals to produce combined signals and a multiplexor which combines said combined signals with said pilot symbols.

7. A cellular mobile telephone system as claimed in claim 6, wherein each channel estimation circuit further comprises:

a signal to interference estimator which receives said second stage estimated carrier signals and produces estimated signal to interference values;

a signal to interference calculator which receives said estimated signal to interference values and produces a signal to interference ratio in response thereto;

an Eb/Io calculator which receives said signal to interference ratio and calculates an Eb/Io ratio in response thereto; and

a power adjustment command generator which generates a control bit for a closed loop power control from Eb/Io said Eb/Io ratio.

8. A cellular mobile telephone system as claimed in claim 1,

wherein said first carrier estimation circuit produces said first stage estimated carrier signals by interpolating a carrier of a data symbol portion other than the pilot symbols.

9. A cellular mobile telephone system as claimed in claim 1, wherein said pre-detection circuit comprises:

a hard decision circuit which performs a hard decision on said data symbol train; and

a multiplexor which multiplexes said data symbol train with said pilot symbols.

10. A cellular mobile telephone system as claimed in claim 9, wherein said hard decision circuit detects said data symbols by a coherent detection.

11. A cellular mobile telephone system as claimed in claim 1,

said second estimation circuit comprises a rotation circuit which receives and rotates said data symbol train and said corresponding receiving signal to produce a rotated output a divider which divides said rotated output into a plurality of groups;

an accumulating and averaging circuit which accumulates and averages each of said groups thereby producing accumulated and averaged sample values; and

an interpolator which interpolates said accumulated and averaged sample values thereby producing said second stage estimated carrier signals.

12. A cellular mobile telephone system as claimed in claim 11,

wherein said rotation circuit multiplies said data symbol train and said corresponding receiving signal with a conjugate value or with said pilot symbols thereby removing modulation of said receiving signal.

13. A cellular mobile telephone system as claimed in claim 11,

wherein said divider divides said rotated output to approximate signals in respective groups to quasi static signals, in periods of said respective groups.

14. A cellular mobile telephone system as claimed in claim 11,

wherein said accumulating and averaging circuit calculates the estimated carrier values of the respective groups by using the accumulation and averaging of the samples to reduce an influence of accompanying noise and interference to thereby improve the estimation performance.

15. A cellular mobile telephone system as claimed in claim 11,

wherein said interpolator interpolates the estimated carrier values given by said accumulating and averaging circuit, to obtain an estimated value of the carrier signal for compensation for fading distortion, diversity-reception, multiplication for synthesis with maximum ratio and actual coherent detection.

16. A cellular mobile telephone system as claimed in claim 11, further comprising:

a signal power estimation circuit which estimates a signal power of said corresponding receiving signal by using said second stage estimated carrier signals; and

an interference power estimation circuit which estimates an interference power of said corresponding receiving signal by using said rotated output and said second stage estimated carrier signals.

17. A cellular mobile telephone system as claimed in claim 16, further comprising:

an Eb/Io calculator which receives said second stage estimated carrier signals and produces a Eb/Io ratio in response thereto; and

a power adjustment command generator which generates a control bit for a closed loop power control based on said Eb/Io ratio.