Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
2001-02-08
2004-08-24
Patel, Ajit (Department: 2664)
Multiplex communications
Communication over free space
Repeater
C370S311000, C455S013400, C455S063100, C455S067130
Reexamination Certificate
active
06781969
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wireless communication systems, and more particularly to a method of preemptively increasing voice and data user's power to protect them against sudden high speed data transmission.
BACKGROUND OF THE INVENTION
Communications systems are known to employ power control methods that control transmission energy of the base station and remote mobile units. A number of different communications systems employ power control, one of which is a Code Division Multiple Access (CDMA) system operating according to Telecommunications Industry Association Interim Standard 95B (IS 95B) protocol. Others include newer generation CDMA 2000 and Universal Mobile Telecommunications System (UMTS) protocols. Power control is used to maintain sufficient communication link quality and information throughput while using minimum power levels in order to maximize system capacity. Reverse-link (mobile or remote unit to base site) power control varies the power level of reverse communication links used by a mobile unit to transmit information to a base site. Forward-link (base site to mobile or remote unit) power control varies the power level of forward communication links used by a base site to transmit information to mobile stations or units.
A CDMA system has a plurality of individual cells or sectors each typically providing a number of dedicated or fundamental channels to transmit low energy and low bit rate voice and data signals. A newer generation of this type of system is designed to also provide a plurality of available supplemental channels adapted for transmitting high speed data signals within the same cells overlying the voice and low speed data signals within the same system infrastructure. One such system is known as wideband CDMA or CDMA 2000. These communication systems utilize an approach in transmitting signals where voice and data signals can be simultaneously transmitted over the air on the same carrier.
Forward link power control for older generation communication systems, such as a CDMA system, is slower than reverse link power control. Power control for newer generation systems, such as UMTS and CDMA 2000, utilizes faster power control on both forward and reverse links. Older CDMA systems typically use forward link quality information feedback transmitted on reverse links to update forward link power levels. This feedback information can be in the form of bits used to indicate whether an individual forward link traffic channel frame was erased. This information can also be in the form of a transmitted message used to indicate that some number of forward link frames were erased during a given time span. Reverse link power control for the older CDMA systems uses a method whereby a power control group is transmitted from the mobile communication unit and received by the base station. The base station compares the energy of the power control group to a set point threshold and instructs the mobile communication unit on a forward link to power up or power down as necessary by transmitting a power adjustment command to the mobile or remote unit. Newer generation systems use power control groups in this manner transmitted between the base station and the mobile unit on both the forward and reverse links. Power control in this manner is used to achieve a desired signal link quality on both the forward and reverse links.
Under normal conditions, this type of closed loop power control will result in sufficient power levels that maintain an interference or noise level of the receive signal at a substantially fixed and acceptable level. However, a call initiated by a remote high speed data (HSD) user within a given sector or cell causes interference that can deteriorate signal quality for other users including both voice and data calls occurring within the cell and neighboring cells. These other users typically operate at minimum power levels necessary to achieve the targeted signal link quality. The new HSD user transmits at a significantly higher power level creating higher levels of system interference. The sudden increase in interference from the high speed data transmission causes erasures for users in this cell and neighboring cells until their power level can be sufficiently increased, which can take on the order of several seconds. This time delay can result in unacceptable lost voice and/or data information for the affected users.
This problem occurs in older IS 95B systems and in newer generation CDMA systems. In a newer generation CDMA system, the sudden HSD transmission occurs over one or more supplemental channels and interferes with existing voice and data users on the fundamental channels and interferes with other data users on supplemental channels in the cell and neighboring cells. In such a system, the high speed supplemental channels are time multiplexed between multiple users. Hence, the channel will typically not always be completely full or completely idle upon the offered load. The channel can have duty cycles in the millisecond range, thus creating the potential for multiple frame erasures per second. This increased frequency of erasures is what contributes significantly to the loss of signal quality or degradation in call quality.
Voice calls or voice data transmissions typically operate at lower transmission speeds, for example, about 9 or about 14.4 Kilobits per second (kbps), and operate at the lowest power necessary to achieve sufficient voice quality. A sudden high speed data transmission by a new HSD user results in interference that can overwhelm the power control algorithms of voice and other existing calls in the particular cell. Therefore, the existing calls must increase their power level multiple times through an algorithm in order to compensate for the new interference caused by one or more HSD calls. During the time the voice calls, for example, are increasing power levels to compensate for the increased level of interference, the frame erasure rate (FER) will rise significantly above voice call target FER values.
The length of time required for the voice calls within a particular cell to increase their power is significant. In one example, a voice call transmits in frames each having a particular time length, such as 20 milliseconds (ms) per frame. For a communication system such as an older generation IS-95B format or newer CDMA 2000 format, a voice call requires at least 12 frames or 240 ms before a second power sense measurement message (PSMM) is sent by the mobile unit indicating that it is receiving erasures. For example, it has been shown that at least one third of voice calls in a particular sector or cell will require at least two power “bump up” messages after each HSD download in that sector in IS-95B systems. Therefore, these mobile units will experience unacceptable FER for at least 240 ms.
Consequently, there is a need for a method to preemptively power up existing voice calls or voice users, as well as other existing users, within a communication system to protect the existing transmissions from the HSD high speed, high power download.
REFERENCES:
patent: 6449461 (2002-09-01), Otten
patent: 6711380 (2004-03-01), Callaway, Jr.
Harris John M.
Nikides Robert S.
Blount Steven A
Motorola Inc.
Patel Ajit
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