Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1998-12-03
2002-04-23
Nguyen, Lee (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000, C370S335000, C370S342000
Reexamination Certificate
active
06377813
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to radiotelephone systems and, in particular, to a radiotelephone system having third generation wideband code division multiple access (WCDMA) capability.
BACKGROUND OF THE INVENTION
A proposed IS-95 third generation (IS-95 3G) radiotelephone system has a wideband, spread spectrum radio interface that uses CDMA technology. The system is expected to meet all of the requirements for the next generation evolution of the current TIA/EIA-95-B family of standards. This includes providing support for the following: a wide range of operating environments (indoor, low mobility, full mobility, and fixed wireless); a wide performance range (from voice and low speed data to very high speed packet and circuit data services); and a wide range of advanced services (including voice only, simultaneous voice and data, data only, and location services). Support is also provided for an advanced Multimedia Quality of Service (QoS) Control capability supporting multiple concurrent voice, high speed packet data, and high speed circuit data services, along with sophisticated QoS management capabilities. A modular structure is proposed to support existing Upper Layer Signaling protocols as well as a wide range of future third generation Upper Layer Signaling protocols. The proposed system is also expected to provide a seamless interoperability and handoff with existing TIA/EIA-95-B systems, and to provide a smooth evolution from existing TIA/EIA-95-B based systems (including support for overlay configurations within the same physical channel as existing TIA/EIA-95-B systems). The proposed system will also support highly optimized and efficient deployments in clear spectrum (in cellular, PCS, and IMT-2000 spectrums), and will offer support for existing TIA/EIA-95-B services, including speech coders, packet data services, circuit data services, facsimile services, Short Messaging Services (SMS), and Over the Air Activation and Provisioning.
In a system operating according to the TIA/EIA-95-B standard a mobile station provides three techniques for output power adjustment (see Section 6.1.2 of IS-95). The three techniques are an open loop estimation based solely on mobile station operation, a closed loop correction that involves both the mobile station and the base station, and an outer loop Frame Error Rate (FER) based technique. In the closed loop and the outer loop correction techniques, the mobile station responds to power control bits received over a forward traffic channel to adjust its output power level.
Power control in a CDMA system is also described in a publication entitled an “Introduction to CDMA and the Proposed Common Air Interface Specification (CAI) for a Spread Spectrum Digital Cellular Standard—An Overview of the Application of Code Division Multiple Access (CDMA) to Digital Cellular Systems and Personal Cellular Networks”, by QUALCOMM Incorporated, Mar. 28, 1992. As is described in this publication, the goal of the mobile station transmitter power control process is to produce, at a cell site receiver or base station, a nominal received signal power from each mobile station transmitter that is operating within the cell. If all mobile stations are so controlled, the end result is that the total signal power received at the cell site from all the mobile stations is equal to the nominal received power times the number of mobile stations. It can therefore be appreciated that the control of the transmitter power is an important consideration when designing mobile stations for operation in the CDMA telecommunications systems.
Of particular interest to the teaching of this invention is the closed loop power control in the forward link transmissions from a base station to a mobile station in the proposed IS-95 3G radiotelephone system. In the IS-95 3G system, power control on the forward link is performed every 1.25 ms or at an 800 Hz refresh rate. As such, a mobile station may request more power or less power for its traffic channels and the power control on the forward link occurs in the base station.
In general, mobile stations employ power control algorithms to determine the power levels required for effective operation. Typically, power control algorithms require that estimates of a traffic channel's signal to noise ratio (SNR) are performed in the mobile station. The SNR and other factors are utilized by the power control algorithm to determine an appropriate power level for effective mobile station operation.
As is known by those skilled in the art, link performance is better with power control for a mobile station moving at a low velocity than for a mobile station moving at a high velocity. These performance observations are presented in a paper entitled “The Evolution of IS-95 to a Third Generation System and to the IMT-2000 Era”, by Edward G. Tiedemann, Jr., Yu-Cheun Jou, and Joseph P. Odenwalder, ACTS Mobile Communications Summit '97, Vol. 2, pages 924-929, dated Oct. 7-10, 1997.
In FIG. 3 of the paper by Tiedemann et al. (reproduced herein as
FIG. 3C
) the traffic channel E
c
/I
or
(dB) to achieve a 1% Frame Error Rate is plotted versus mobile station velocity. As is illustrated in
FIG. 3C
, link performance is better with power control for a mobile station travelling at a low velocity than for a mobile station travelling at a high velocity, as compared to the case where there is no power control. A mobile station travelling at a high velocity is generally experiencing shifts in a carrier frequency due to the relative motion between the mobile station and the base station. This shifting in frequency is well known to those skilled in the art as the Doppler effect of wave propagation between non-stationary points. As a result, a mobile station travelling at a low velocity can be referred to as a mobile station in a low Doppler condition, and a mobile station travelling at a high velocity can be referred to as a mobile station in a high Doppler condition.
There are several possible reasons for the degradation of link performance in mobile stations moving at a high velocity (i.e. in a high Doppler condition), for example, a velocity greater than about 30 km/h for a carrier frequency of 2 GHz in a PCS band (actually about 1.86 GHz). These possible reasons include, for example, the fact that the channel is changing too fast for the mobile station to accurately estimate the channel response, and the fact that delays occur within the closed loop power control process. The delays in the closed loop power control process may be due to delays between the channel measurement performed at the mobile station and the actual change in power at the base station. Other delays may be experienced at the base station as the base station extracts and processes information from the channel. For example, the mobile station performs processing operations to determine whether or not the mobile station requires more or less power and then transmits a power control command on the reverse link to the base station. The base station decodes the command received over the reverse link and then applies the power control command to change the power of the traffic channel.
The gain due to closed loop power control, expressed as the ratio of the energy of an information bit (E
b
) to the noise power spectrum density (N
t
) or E
b
/N
t
, can be as large as 2-6 dB for low Doppler conditions (e.g., less than 50 Hz in the PCS band (2 GHz)) for mobile stations moving at a velocity of less than about 30 km/h, and as much as about 60 km/h in the cellular band (1 GHz, actually about 800-900 MHz). In high Doppler conditions (e.g., in the PCS band for mobile stations moving at a velocity above about 30 km/h, and over about 60 km/h in the cellular band), the closed loop power control results in degraded E
b
/N
t
performance, with the degradation being as large as 1-2 dB.
It can thus be appreciated that it would be desirable to have a power control technique which combats the effects of fading in both the low and the high Doppler conditions, and which enable
Kansakoski Antti
Tran Jean-Marie
Nguyen Lee
Nokia Corporation
Perman & Green LLP
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