Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-07-26
2004-03-09
Pezzlo, John (Department: 2662)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S329000, C370S252000, C370S437000, C455S450000
Reexamination Certificate
active
06704328
ABSTRACT:
TECHNICAL FIELD
The present invention relates to communications systems in general and, more particularly, to a method and apparatus for smoothly transmitting bursty data in a wireless communications system and a corresponding signalling method.
BACKGROUND INFORMATION
Existing CDMA (code-division multiple access) systems based on TIA/EIA standard IS-95 support the transmission of digital information at rates of up to 9.6 Kbps or at most 14.4 Kbps per channel. However, these data rates are considered to be insufficient for supporting many emerging data transfer applications, including browsing of the World Wide Web, electronic mail, e-commerce, tele-medicine and the like. With the goal of providing greater flexibility in the delivery of data services while continuing to exploit the features and merits of a CDMA-based system, various North American, European and Japanese consortia have developed proposals for what has become known as third generation (3G) CDMA.
As a consequence of 3G CDMA being able to support a wide range of data rates, links having different data rates may vary considerably in the power they consume. For example, to maintain the same quality of service for a 384 Kbps link, approximately 16 dB more power is required than for a 9.6 Kbps link. (The latter is typical of the bit rate of a standard voice channel in both IS-95 and 3G CDMA, while the former is typical of the bit rate that has been proposed for use by high-speed data channels in 3G CDMA.) Thus, the abrupt start of a 384 Kbps transmission is roughly equivalent to the simultaneous origination of 40 voice calls.
The interference caused by establishing high-speed data connections depends on various factors, such as the locations of the users in a cell, the direction of communication (forward-link or reverse-link) and the cell loading. By way of illustration, let there be a high-speed link established between a first mobile unit and a base station in a cell C
1
. If a second mobile unit is also located in cell C
1
and if the first mobile unit's high-speed connection is in the forward-link direction, then very little interference will be felt by the second mobile unit, due to mutual orthogonality of the signals transmitted by the base station in cell C
1
.
On the other hand, if the second mobile unit is located in a cell C
2
which borders with cell C
1
and if the first mobile unit's high-speed connection has been established in the forward-link direction, then factors such as the loading of cell C
2
and the proximity of the second mobile unit to the boundary of cell C
1
will determine the level of interference felt by the second mobile unit. This can range from very mild (when cell C
2
is heavily loaded and the second mobile unit is far away from the boundary between cells C
1
and C
2
) to very severe (when cell C
2
has very few active calls and the second mobile unit is proximate the boundary between cells C
1
and C
2
).
An increase in the interference felt by other users (e.g., the second mobile unit in the above example) results in a degradation in the quality of service of the connections established by those other users. Consequently, the transmitted power of the affected links will be increased using standard power control algorithms until an acceptable quality of service is again attained. However, the other users may not be able to increase their power levels quickly enough, which may result in frames being lost or delayed in the meantime. Specifically, if there is an overlay of the 2G and 3G systems, the users of the 2G system will suffer loss of a greater number of frames. Fast power control is not employed in 2G systems. The 2G users will require a longer time to respond to the increase in the interference level.
Furthermore, even if the other users are capable of raising their power levels quickly, a certain amount of time will elapse before stable power levels are arrived at by the various users. This is due to the fact that when link power is increased to satisfy any one user, interference will be caused to the remaining users, who then have to raise their respective link power, thereby affecting the user who originally required an increase in link power, and so on. This chain reaction continues until all users reach a stable power level but in the meantime, some users may experience a lower signal quality than required. Depending on the degree of burstiness of the high-speed data, such chain reactions may be initiated many times per second and thus the power levels may not be given a chance to converge.
Clearly, a development problem of the 3G CDMA systems is that of addressing the sudden interference changes resulting from the bursty nature of high-speed data transmissions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved method and apparatus for smoothly transmitting bursty data in a wireless communications system.
According to one aspect of the present invention, there is provided a method of smoothing bit rate transitions in a bursty input data stream arid providing an output data stream having smoother data rate transitions than the input data stream, the method comprising the steps of: receiving the input data stream in data store means; providing a rate control signal with reference to a control message containing system parameters; and withdrawing the data from the data store means at a rate determined by the rate control signal.
According to another aspect of the present invention, there is provided a transmission system comprising: data source means for providing an input data stream comprising data bursts; data store means for receiving the input data stream; control means for providing a rate control signal in responsive to a control message; and processing means for withdrawing data from the data store means at a rate indicated by the rate control signal, so as to produce an output data stream which is less bursty than the input data stream.
According to another aspect of the present invention, there is provided a wireless-link communications system comprising signal transmitter and receiver, the transmitter comprising: data source means for providing an input data stream comprising data bursts; data store means for receiving the input data stream; control means for providing a rate control signal in responsive to a control message; processing means for withdrawing data from the data store means at a rate indicated by the rate control signal, so as to produce an output data stream which is less bursty than the input data stream; and transmission means for transmitting a signal in response to the output data stream to the receiver over a wireless link, the receiver comprising: receiving means for the signal from the transmitter; reproducing means for reproducing the data from the signal received by the receiving means.
For example, the control message is sent to a receiver to communicate for power ramp-up and ramp-down profiles. The control message contains a plurality of assignments. Each assignment comprises a plurality of fields, each field having a group of parameter data. The parameter data includes rate and time period information. The rate of the rate control signal is varied in response to the rate information of the parameter data. The rate of the rate control signal is set during the time period determined by the time period information of the parameter data. The data is withdrawn from the data store means at the rate set in response to the rate control signal. Smoothing the bursty data stream reduces the degradation of service quality to other users of the system upon establishing the bursty connection. The problems related to convergence of power levels across the entire system are practically eliminated, as well.
The transmission system may comprise transmitter means for scaling the output of the processing means with reference to a variable power of the rate control signal provided by the control means. In a case where the transmission system is implemented in a wireless communications system, after a high da
Fong Mo-Han
Khaleghi Farideh
Larijani Parsyna R.
Matyas Robert
Senarath Nimal G.
Nortel Networks Limited
Pezzlo John
LandOfFree
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