Filtering method to allow FDD and TDD operation in PCS...

Details Filtering method to allow FDD and TDD operation in PCS... Filtering method to allow FDD and TDD operation in PCS...

1998-05-08

2001-04-03

Chin, Wellington (Department: 2664)

Multiplex communications

Duplex

Communication over free space

C370S280000, C370S330000, C370S489000, C455S076000

Reexamination Certificate

active

06212172

ABSTRACT:

FIELD OF THE INVENTION
The field of the invention pertains to wireless communication transreceivers including, more particularly, transreceivers capable of FDD and TDD operation.
DESCRIPTION OF RELATED ART
One method of providing duplex communication is through use of FDD (Frequency Division Duplex) protocols in which frequency allocations in the PCS band is split into a forward sub-band and a reverse sub-band. This split can accommodate FDD where transmission is limited to one of the sub-bands. However, this split presents a problem to coexisting TDD (Time Division Duplex) systems which transmit and receive on the same frequency and can use either of the frequency sub-bands for transmission.
Shown in
FIG. 1
is a known implementation of a TDMA-FDD system, such as PCS-1900 or IS-136 with a switch placed between the radio and the antenna. The switch, placed before the forward and reverse channel filters, selectively routes the RF signal path either to the receiver or from the transmitter in response to the mode of the transreceiver (either transmit or receive). The receiver subsystem will typically employ a bandpass filter tuned to the forward channel, and the transmitter subsystem will typically employ a filter tuned to the reverse channel. As a result of this switch placement, only the forward channel path or only the reverse channel path may be selected. This configuration precludes transmission and reception in both the forward channel frequency band or the reverse channel frequency band, thereby limiting the available frequency bands for a TDD system. Other known implementations remove the switch entirely to allow simultaneous transmit and receive (e.g., IS-54 and IS-19) but are still limited to different frequencies.
While a transreceiver operable in FDD or TDD could employ duplexers, or dual filters, for FDD operation plus an additional filter and switch for TDD operation, since either the TDD or FDD mode uses its own set of filters, one set of components will be under utilized rendering the system cost inefficient.
SUMMARY OF THE INVENTION
The present invention comprises a transreceiver architecture that allows a common set of filters to be used for either FDD (Frequency Division Duplex) or TDD (Time Division Duplex) operation in a given range of frequencies, thereby reducing circuitry count and implementation costs. Accordingly, the present invention allows operation in a full or half-duplex TDD or FDD system.
In a preferred embodiment of the invention, switches are incorporated after the forward and reverse channel filters to create three paths controlled by predetermined logic. This configuration permits use of both the forward and reverse channel filters for a TDD system and combines the forward and reverse channel filters to create a filter that can pass both frequency sub-bands. These single device frequency duplexers are often commercially available, thereby allowing for ease in implementation and cost reduction.
Some frequency allocation plans, such as those in the USA, often have a frequency band between the transmit and receive regions. In the USA, this frequency band can be referred to as the “unlicensed frequency band” and can be used for TDD only. An alternative preferred embodiment comprises an additional filter to allow exploitation of multiple frequency bands for transmission and reception.


REFERENCES:
patent: 5475677 (1995-12-01), Arnold et al.
patent: 5809395 (1998-09-01), Piercy et al.
patent: 5933421 (1999-08-01), Alamouti et al.
patent: 6118984 (1998-09-01), Yu-Hong

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