SYSTEM AND METHOD FOR FREQUENCY OFFSETTING OF INFORMATION COMMUNICATED IN MIMO-BASED WIRELESS NETWORKS

• US 20090180466A1
• Filed: 02/20/2009
• Published: 07/16/2009
• Est. Priority Date: 04/07/2006
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: BelAir Networks (Telefonaktiebolaget LM Ericsson)
• Inventors: Soul, Colin H., Rayment, Stephen G., Smith, Roland A.
• Granted Patent: US 8,254,865 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: H03J 7/04 where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 2027/0028 at passband only
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657

Abstract

A communications system includes a multiple-input/multiple-output (MIMO) architecture for high capacity switched mesh networks. The MIMO architecture has a plurality of radio frequency chains. One of the plurality of radio frequency chains is configured to apply a first frequency offset to a base frequency of an output signal to generate a first transmitting frequency; and another of the plurality of radio frequency chains being configured to apply a second frequency offset to the base frequency to generate a second transmitting frequency. The system uses the carrier frequency offset to lock the clock of the master subsystem to the clock of the slave subsystem, thereby enabling bandwidth expansion to be employed on the MIMO data streams.

Claims

1. A method of synchronizing a receiver with a transmitter in a communications system comprising a multiple-input/multiple-output (MIMO) architecture, the architecture comprising a first and a second radio frequency chain, the communications system being configured to transceive at least two signals having a predetermined frequency separation, and the method comprising the steps of:

a) locking a frequency of the receiver to an external timing reference; and

b) locking a frequency of the transmitter to the external timing reference,

wherein each of steps a) and b) is carried out independently of one another.

2. The method of claim 1, wherein the external timing reference comprises a Global Positioning System (GPS) timing reference.

3. The method of claim 2, wherein the GPS timing reference is configured to lock a variable crystal oscillator.

4. The method of claim 3, wherein the variable crystal oscillator comprises a 40-MHz variable crystal oscillator.

5. The method of claim 2, wherein the GPS timing reference is configured to lock a plurality of transceivers such that the method is usable in any of a point-to-point application, a point-to-multipoint application, and a multipoint-to-multipoint application.

6. The method of claim 1, wherein the external timing reference comprises an IEEE 1588 timing reference.

7. The method of claim 5, wherein the IEEE 1588 timing reference is configured to lock a variable crystal oscillator.

8. The method of claim 7, wherein the variable crystal oscillator comprises a 40-MHz variable crystal oscillator.

9. The method of claim 6, wherein the IEEE 1588 timing reference is configured to be frequency locked to a GPS timing reference.

10. The method of claim 6, wherein the IEEE 1588 timing reference is configured to be frequency locked to a Building Integrated Timing Source (BITS) reference.

11. The method of claim 6, wherein the IEEE 1588 timing reference is configured to lock a plurality of transceivers such that the method is usable in any of a point-to-point application, a point-to-multipoint application, and a multipoint-to-multipoint application.

12. A method of synchronizing a receiver with a transmitter in a communications system comprising a multiple-input/multiple-output (MIMO) architecture, the architecture comprising a first and a second radio frequency chain, the receiver being connected to a controller, the communications system being configured to transceive at least two signals having a predetermined frequency separation, and the method comprising the step of locking a frequency of the receiver to a frequency of the transmitter by configuring the controller to perform the steps of:

a) using a packet transmitted by the transmitter and received by the receiver to generate a carrier frequency offset (CFO) estimate;

b) adjusting the receiver reference frequency based on the CFO estimate; and

c) repeating steps a) and b) until the generated CFO estimate is substantially equal to zero.

13. The method of claim 12, wherein the controller comprises at least one of an open-loop controller;

a closed-loop controller;

a proportional controller;

an integral controller;

a derivative controller; and

a Kalman filter.

14. A method of synchronizing a receiver with a transmitter in a communications system comprising a multiple-input/multiple-output (MIMO) architecture, the architecture comprising a first and a second radio frequency chain, the transmitter being connected to a controller, the communications system being configured to transceive at least two signals having a predetermined frequency separation, and the method comprising the step of locking a frequency of the transmitter to a frequency of the receiver by configuring the controller to perform the steps of:

a) using a packet transmitted by the receiver and received by the transmitter to generate a carrier frequency offset (CFO) estimate;

b) adjusting the transmitter reference frequency based on the CFO estimate; and

c) repeating steps a) and b) until the generated CFO estimate is substantially equal to zero.

15. The method of claim 14, wherein the controller comprises at least one of an open-loop controller;

a closed-loop controller;

a proportional controller;

an integral controller;

a derivative controller; and

a Kalman filter.

16. A method of synchronizing a receiver with a transmitter in a communications system comprising a multiple-input/multiple-output (MIMO) architecture, the architecture comprising a first and a second radio frequency chain, the receiver being connected to a controller, the communications system being configured to transceive at least two signals having a predetermined frequency separation, and the method comprising the step of locking a frequency of the receiver to a frequency of the transmitter by configuring the controller to perform the steps of:

a) using a packet transmitted by the transmitter and received by the receiver to determine an error associated with the transmitted packet;

b) adjusting the receiver reference frequency based on the determined error; and

c) repeating steps a) and b) until the determined error is substantially equal to zero.

17. A method of synchronizing a receiver with a transmitter in a communications system comprising a multiple-input/multiple-output (MIMO) architecture, the architecture comprising a first and a second radio frequency chain, the receiver being connected to a controller, the communications system being configured to transceive at least two signals having a predetermined frequency separation, and the method comprising the step of locking a frequency of the receiver to a frequency of the transmitter by configuring the controller to perform the steps of:

a) using a packet transmitted by the transmitter and received by the receiver to determine an error associated with the transmitted packet;

b) adjusting the receiver reference frequency based on the determined error;

c) using a retransmission of the received packet to determine an updated error associated with the retransmitted packet; and

d) repeating steps b) and c) until the determined updated error is substantially equal to zero.

18. A method of synchronizing a receiver with a transmitter in a communications system comprising a multiple-input/multiple-output (MIMO) architecture, the architecture comprising a first and a second radio frequency chain, the communications system being configured to transceive at least two signals having a predetermined frequency separation, and the method comprising the steps of:

a) locking a frequency of the receiver to a first high precision reference frequency; and

b) locking a frequency of the transmitter to a second high precision reference frequency,

wherein each of the first and second high precision reference frequency employs a reference crystal having a maximum frequency error of plus-or-minus 5 parts per million.