Microcellular communications system using space diversity reception

• US 5,067,173 A
• Filed: 12/20/1990
• Issued: 11/19/1991
• Est. Priority Date: 12/20/1990
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.)
• Original Assignee: AT&T, Inc.
• Inventors: Gordon, Alexander, Vella-Coleiro, George P.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US07/630,674
• Time in Patent Office: 334 Days
• Field of Search: 455/617, 455/33, 455/54, 455/137, 455/273, 455/275, 455/139, 455/607, 455/609, 455/606, 455/610, 455/612, 379/59, 379/60, 343/844
• US Class Current: 398/116
• CPC Class Codes: H04B 7/084 Equal gain combining, only phase adjustments antenna beam scanning or forming by phase or amplitude control H01Q3/26, e.g. phased arrays
• CPC Class Codes: H04L 1/06 using space diversity

Abstract

Microcellular stations are transceiving units covering a relatively small geographic area and adapted to establish bidirectional links between mobile telephone subscriber stations and a main base station. Each such microcellular station includes a transmitter for generating outgoing signals directed to the main base station over an optical fiber link. Radio signals received from a mobile station at a separate diversity antenna of the microcellular station are frequency shifted and combined with other signals received from the mobile station. The transmitter at the microcellular station generates an optical carrier signal which is modulated by the resulting combined signals. A frequency converter, located at the main base station, restores the frequency band of signals received from the microcellular station to its original frequency. Frequency shifting and conversion are implemented at the microcellular station and at the main base station by frequency mixing steps performed by oscillators at both locations, which oscillators use the same reference frequency thereby achieving channel coherency.

Claims

1. A microcell communications station exhibiting receive space diversity comprising:

a first and a second antenna for each receiving radio signals in a predetermined range of radio frequencies;

frequency conversion means coupled to the second antenna for shifting the frequency range of signals received at the second antenna;

combining means coupled to the first antenna and the frequency conversion means for generating combined signals in two different frequency bands; and

means coupled to the combining means for generating a carrier signal modulated by the combined signals.

2. A microcell communications station according to claim 1, wherein the frequency conversion means comprises a frequency down converter including a mixer and a local oscillator having a frequency selected to substantially reduce unwanted mixing products within the microcell station predetermined range of receive radio frequencies.

3. A microcell communications station according to claim 2, wherein the frequency of the local oscillator is substantially below the frequency band of the receive radio signals.

4. A microcell communications station according to claim 1, wherein the carrier signal generating means comprises a single laser transmitter for generating an optical wavelength signal.

5. Method for processing radio signals at a microcell communications station comprising the steps of:

receiving at the microcell station first and second radio signals having respective frequencies within a first range of frequencies;

shifting the frequency range of the received second radio signals to generate third radio signals having frequencies within a second range of frequencies;

combining the first radio signals and the third radio signals to generate combined signals having frequencies in the first and second ranges of frequencies; and

modulating the combined signals on a carrier signal.

6. Method according to claim 5, wherein the shifting step comprises the step of down converting the frequency of the second radio signals so that the second range of frequencies is lower than the first range of frequencies.

7. Method according to claim 6, wherein the down converting step comprises the step of mixing the received second radio signals with a signal generated by a local oscillator having a frequency substantially below the frequency band of the receive radio signals.

8. Method according to claim 7, comprising the step of selecting the frequency of the local oscillator to substantially reduce unwanted mixing products within the band of the receive radio signals.

9. A microcell mobile radio communications station exhibiting receive space diversity comprising:

a first antenna for receiving radio signals in a first range of radio frequencies;

a second antenna for receiving radio signals in the first range of radio frequencies;

frequency conversion means coupled to the second antenna for reducing the frequency range of signals received at the second antenna;

combining means coupled to the first antenna and the frequency conversion means for generating combined signals in two different frequency bands; and

a laser transmitter coupled to the combining means for generating an optical wavelength carrier signal modulated by the combined signals.

10. A microcell mobile radio communications station according to claim 9, wherein the frequency conversion means comprise:

a high level termination-insensitive mixing circuit; and

a local oscillator coupled to the mixing circuit and having a frequency selected to substantially reduce unwanted mixing products within the range of the receive radio signals.

11. A microcell mobile radio communications station according to claim 10, wherein the frequency of the local oscillator is substantially below the frequency band of the receive radio signals.

12. A microcellular communications system comprising:

a first antenna for receiving radio signals in a first range of radio frequencies;

a diversity antenna for receiving radio signals in the first range of radio frequencies;

frequency down conversion means coupled to the diversity antenna for reducing the frequency range of signals received at the diversity antenna;

combining means coupled to the first antenna and the frequency conversion means for generating combined signals in two different frequency bands;

a laser transmitter coupled to the combining means for generating an optical wavelength carrier signal modulated by the combined signals; and

an optical transmission path coupled to the laser transmitter for transmitting the optical carrier signal to a remote cellular base station.

13. A microcellular communications system according to claim 12, wherein the remote cellular base station includes frequency up conversion means for increasing the frequency range of the signals received over the optical transmission path to the first range of radio frequencies.

14. A microcellular communications system according to claim 13, wherein the frequency down conversion means and the frequency up conversion means each includes a mixing circuit and a local oscillator using the same reference frequency.

15. A cellular communications base station comprising:

input means adapted to receive signals in two different frequency bands from a remote cellular base location;

detecting means coupled to the input means for demodulating the received signals;

means coupled to the detecting means for dividing the demodulated signals into two separate signals;

frequency shifting means coupled to the dividing means for increasing the frequency range of one of said separate signals;

first filtering means coupled to the frequency shifting means for filtering the frequency-increased separate signals; and

second filtering means coupled to the dividing means for filtering the other separate signal.