Multi-band receiver having multi-slot capability

Details Multi-band receiver having multi-slot capability Multi-band receiver having multi-slot capability

2002-10-21

2004-10-12

Appiah, Charles (Department: 2686)

Multiplex communications

Communication techniques for information carried in plural...

Combined time division and frequency division

C455S552100, C455S315000, C455S189100, C455S190100, C455S323000

Reexamination Certificate

active

06804261

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to radio or wireless communications and, more particularly, relates to a multi-band receiver having multi-slot capability.
BACKGROUND OF THE INVENTION
Wireless or radio frequency (RF) communication systems are an integral component of the ongoing technology revolution and are evolving at an exponential rate. Many wireless communication systems are configured as “cellular” systems, in which the geographic area to be covered by the cellular system is divided into a plurality of “cells”. Mobile communication devices or stations (e.g., wireless telephones, pagers, personal communications devices and the like) in the coverage area of a cell communicate with a fixed base station or transmitter within the cell. Low power base stations are utilized, so that frequencies used in one cell can be re-used in cells that are sufficiently distant to avoid interference. Hence, a cellular telephone user, whether mired in traffic gridlock or attending a meeting, can transmit and receive phone calls so long as the user is within a cell served by a base station.
The communication format used in most wireless communications systems is a high-frequency carrier waveform modulated by low frequency or “baseband” audio or data signals. Mobile stations (wireless handsets, for example) within a wireless communication system typically have a transmitter that “modulates” baseband signals (e.g., speech detected by the handset microphone) onto the carrier waveform. Amplitude modulation (AM) and frequency modulation (FM) techniques, for example, are well known to those of ordinary skill in the art. Mobile stations also typically have a receiver that “demodulates” the carrier waveform to extract the baseband signal. The carrier waveforms required for modulation and demodulation are high frequency, periodic waveforms and are typically generated by oscillators within the transmitter and receiver.
The available frequency spectrum is distributed among the cellular base stations according to a frequency plan. In a GSM network, for example, the transmission band covers 880-915 MHz and the receiving band covers 925-960 MHz (see detailed description herein and FIGS.
2
-
3
). The transmit and receive bands, in turn, are partitioned into 200 kHz frequency channels. Many of these channels, obviously, are reserved for the actual transmission and reception of speech or data. These channels are known as “traffic” channels. Other channels are reserved for control and monitoring operations. These channels are known as “broadcast” channels. Information may be exchanged in slots tuned to broadcast channels about, for example, whether a hand over to a neighboring cell should be performed, or which traffic channel the mobile station should tune to next.
GSM networks use a time-division multiple access (TDMA) architecture. Each channel (within the transmit and receive bands) is available to multiple users, but at different times. In one TDMA implementation, each channel is subdivided in time into eight time slots. Hence, each frequency channel will be available to eight different transceivers or users at different times. Each time slot has a duration of approximately 0.577 ms (577 &mgr;s), and eight time slots form a TDMA “frame”, having a duration of 4.615 ms.
An example TDMA frame
80
having eight time slots 0-7 is illustrated in
FIG. 1
a
. Frame
80
represents the channel/time assignments for one wireless device or mobile station. Slot zero is a traffic slot in which data is transmitted over a traffic channel, and slot three is also a traffic slot in which data is received over a traffic channel. Time slot six has been reserved as a monitor slot. In monitor slot six, the wireless device may monitor a broadcast channel for operational/control data, an adjacent cell for power information, or any other frequency on which control or operational data is exchanged.
Since the device must be tuned to different frequency channels in the traffic and monitor slots, a certain amount of resting time is required to permit retuning and settling of the oscillator. The unused or “rest” time slots (slots
1
,
2
,
4
and
5
in frame
80
, for example) between traffic and monitor slots are used to retune and settle the local oscillator to the next frequency channel. The tuning and settling time required in a conventional GSM receiver, in order to guarantee reprogramming of the oscillator over the frequency range extremes and locking within 100 Hz, is in the range of 840 ms (about 1.5 slots). In a frame structure such as frame
80
, where the traffic and monitor slots are single and spaced apart, ample rest slots are available to accommodate this requirement.
One of the current development trends in GSM systems is “multi-slot” reception and transmission. In multi-slot operation, a mobile station transmits and/or receives in multiple time slots within each TDMA frame. This is in contrast to the configuration of frame
80
, in which there is only one receive and one transmit slot per frame. A multi-slot framework, by providing more receive and/or transmit slots per frame, drastically increases data transmission rates. Increased data transmission rates are particularly important for data-intensive applications such as wireless Internet access.
The present invention is directed to a mobile station having multi-slot reception capability. A TDMA frame
85
having multiple traffic and monitor slots within the receive band is shown in
FIG. 1
b
. TDMA frame
85
has one transmit traffic slot zero, two receive traffic slots two and three, and three monitor slots four through six. Many other multiple slot assignments are of course possible. Frame
85
is just one possibility that is presented for exemplary purposes only.
Use of multiple slots is problematic in conventional receivers as there is often insufficient time to retune and settle the local oscillator when switching frequencies between traffic and monitor slots. In
FIG. 1
b
, for example, there is only one slot available to switch from the transmit traffic channel to the receive traffic channel, and no slots are available to make the switch from the receive traffic channel to the receive monitor channel. For the latter frequency change, where adjacent slots are assigned to different frequency channels, the required oscillation frequency change must be effected virtually simultaneously.
Various attempts have been made to decrease the frequency channel switching time in order to accommodate multi-slot reception. One approach has been to increase the corner frequency of the receiver's PLL loop filter in order to decrease the lock time of the PLL. This approach, however, decreases the utility of the filter and makes it difficult to meet spurious performance requirements. Another approach is to use fractional-N type architectures, which permit use of higher PLL reference and corner frequencies. Fractional-N architectures, however, still pass high levels of phase noise and, though they provide quicker lock times, they do not provide the speed that is necessary for instantaneous switching. Another approach is to simply use separate high frequency oscillators in the receiver for the traffic and monitor channels. This approach, though providing the necessary speed, is too costly to make its implementation feasible.
SUMMARY OF THE INVENTION
The present invention provides a multi-band receiver for a wireless communication device that has enhanced multi-slot reception capability. The inventive receiver provides virtually instantaneous frequency channel switching by mixing a pre-existing oscillation resource with an added low frequency oscillator. The added oscillator and mixer elements are inexpensive, can be integrated with the pre-existing components on one IC, and contribute a minimal amount of current drain to the receiver.
In one embodiment of the present invention, a receiver is provided. An antenna receives an Rx signal, and a first oscillator generates a relatively high frequency traffic LO signal. Second and third oscillators ge

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