Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/06—TPC algorithms
  • H04W52/14—Separate analysis of uplink or downlink
  • H04W52/146—Uplink power control
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/30—TPC using constraints in the total amount of available transmission power
  • H04W52/32—TPC of broadcast or control channels
  • H04W52/325—Power control of control or pilot channels
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/38—TPC being performed in particular situations
  • H04W52/50—TPC being performed in particular situations at the moment of starting communication in a multiple access environment
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/30—TPC using constraints in the total amount of available transmission power
  • H04W52/32—TPC of broadcast or control channels
  • H04W52/322—Power control of broadcast channels

Definitions

• the present invention relates to cellular communication systems and, more particularly, to a system for increasing the reliability of the cellular communication system in environments having a large number of mobile telephone units simultaneously attempting to access a base station.
• each transmitter may transmit a message at any time. Upon discovering that the transmitted message has collided, the transmitter waits a random delay time and retransmits the message. In Slotted Aloha, all messages fit into a time slot of a predetermined length. Upon discovering that the transmitted
• the transmitter delays a random number of slots and then retransmits the message.
• a random delay is introduced to prevent transmitters from retransmitting simultaneously.
• CDMA code division multiple access
• Each mobile station has a pseudo noise (PN) code uniquely associated with it that the mobile station uses to spread its transmitted signals, commonly referred to as the long PN code.
• PN pseudo noise
• the base station can receive and despread the signal transmitted by the mobile station.
• the mobile station can receive and despread the signal transmitted by the base station.
• the signals may be modulated with a pilot PN code as well.
• the message transmitted by a mobile station attempting to initiate a call is one example of such a transmission.
• a mobile station wishing to initiate calls can transmit such requests on a common access channel using a corresponding common PN code.
• the base station can monitor the access channel by despreading of the signal using this PN code.
• the access channel is used because messages such as those initiating a call are relatively short in comparison to voice transmission, and a receiver can more easily monitor a relatively few access channels than the large number of unique traffic channels with which the mobile stations are associated by the unique PN long codes.
• the transmissions arrive at the base station separated in time by a delay. Under most operating conditions, it is unlikely that a large number of mobile stations will be at the same distance from the base stations. However, simultaneously transmitted messages would collide if two or more are at the same range. Under most conditions, the base station can distinguish among the transmissions because the time between arrivals of the transmissions at the base station exceeds one PN chip.
• the probability of access channel collisions increases with an increase in the number of mobile stations and with an increase in multi-path reflections.
• Multi- path compounds the problem because, while the main signals of two transmissions may be separated in time by more than one chip, multi-path components of the transmissions may not be.
• the reverse access channel employs slotted Aloha as the access protocol.
• 3G systems i.e. CDMA 2000
• possible enhancements to the existing access procedure include fast closed loop power control which provides up to 5 dB Eb/No reduction relative to IS 95B open loop power control.
• the power control bits on the forward link are transmitted on a common power control channel (F-PCCH). Since access transmissions are short, typically around 100 ms, fast response is required for power control to be effective.
• F-PCCH common power control channel
• the pseudo noise (PN) randomization procedure in IS 95 A/B allows the mobile station to delay its long code timing by a random number of chip durations between 0 and 511. If two mobile stations initiate access attempts in the same slot of the same reverse access channel (RACH), but with sufficient chip separation between them due to PN randomization, both transmissions may be successfully decoded by the base station. However, both mobile stations will now be power controlled by a single power control bit stream on the F-PCCH associated with the particular RACH on which the mobile station preambles were detected. If the base station is able to identify more than one transmission, it may choose to follow the strongest mobile station, randomly toggle power control bits up and down and effectively not have power control.
• RACH reverse access channel
• the transmit powers of the accessing mobile stations listening to the same power control bit stream are a random walk with 1 dB steps. If unchecked, this random walk may introduce serious interference in the system, in that the random walk is a function of load and slot duration. In either case, associating power control bit streams on the F- PCCH with a particular RACH does not ensure unambiguous power control.
• FIG. 1 shows a timing diagram illustrating access channels for two mobiles and a fast power control channel
• FIG. 2 shows a functional flow diagram depicting the process of providing fast power control to mobile stations simultaneously initiating a random access transmission to a base station according to the method and the system of the present invention.
• each R-RACH Message comprises a preamble portion, followed by a header portion, followed by a message or data portion.
• the frame duration for the R-RACH header is 5 ms in duration.
• transmissions on the R-RACH are slotted, with the slot interval on a given R- RACH being defined by the system parameter RACH_SLOT.
• each RACH_SLOT is 1.25 ms.
• the mobile stations Ml and M2 listen to the power control bits based upon the RACH_SLOT number. A power control bit is sent every 1.25 ms on the F-PCCH to signal the mobile station to increase or decrease its transmit power by a predetermined amount. The mobile station adjusts its transmit power every 1.25 ms (i.e. every power control group). The actual timing of F-PCCH may be delayed for a predetermined number of power control groups, thereby allowing the base station to detect the preamble as discussed in greater detail below.
• the number of available power control bits on the F-PCCH in a single power control group is 24. Therefore, each F-PCCH can support 24 simultaneous access attempts.
• a single power control bit assigned in every power control group yields a power control rate of 800 bits per second.
• a single power control bit every alternate power control group yields a rate of 400 bits per second, etc.
• IS 95B access procedures limit the maximum PN randomization offset to 512 chips.
• the mobile station uniformly delays the long code timing and the I and Q pilot PN sequences.
• the base station searcher has to search for a preamble on the RACH long code and all possible offsets up to 512 chips.
• the present invention proposes to parameterize the maximum possible offset to N chips, and define allowed offset slots or sub-channels - in other words, the notion of slotting the PN randomization interval into "sub-channels".
• Each offset slot is M chips long. M is large enough to account for cell radius and worst case multipath.
• each accessing mobile station delays its transmit timing and the long code generator state in discrete steps.
• N/M 512.
• Each F-PCCH sub-channel is associated with each R-RACH slot through a non-random hash procedure.
• Each R-RACH slot has a different long code as discussed above. If the base station detects an access preamble in any R-RACH slot, it starts a power control bit stream on the associated F-PCCH sub-channel.
• FIG. 2 is a flow diagram depicting a method for providing fast power control to mobile stations simultaneously initiating random access transmission to a base station in accordance with the present invention.
• the process may be initiated whenever the mobile station (not shown) must send information to the base station on a common access channel. For example, a user may initiate a telephone call, which must be routed to the base station.
• the flow begins at reference numeral 202, wherein prior to initiating a transmission, the mobile station randomly selects one of the available R_RACHs. In addition, the mobile station receives the ID of the associated F-CACH, F-PCCH, and F-CCCH in a broadcast message from the base station.
• the step of PN randomization is performed, wherein the mobile station time delays its access channel transmissions by a small amount that is greater than or equal to one chip, but is much less than the length of the message itself, as is well known in the art.
• the step of transmitting a Message comprising a preamble, a header, and a message or data portion in the next R- RACH slot with index i is performed.
• a response to the power control bits given by the associated F-PCCH is given.
• the power control sub-channels on the associated F-PCCH are determined by the R-RACH slot index i.
• an acknowledgment i.e. detection acknowledgment
• F- CACH Forward Common Assignment Channel
• the mobile station fails to receive the detection acknowledgment within a timeout period, it will abort transmission and perform a random backoff and power adjustment as shown at reference numeral 212 and as is well known in the art. It should be noted that the power adjustment described at reference numeral 212 should not be confused with fast power control. Thereafter, flow reverts back to the start. Possible causes for non-receipt of the detection acknowledgment include the preamble not being detected, or an error in the detection acknowledgment message itself. However, it should be noted that the mobile station does not wait for the detection acknowledgment message to transmit the header/message portion and respond to power control bits on the associated F-PCCH sub-channel.
• the detection acknowledgment message is associated with a successful preamble detection on a sub-channel, and not with successful decoding of the access Message.
• the mobile station If the mobile station does not receive the decode acknowledgment, then the mobile will perform a random backoff and power adjustment as shown at reference numeral 218 and as is well known in the art. It should be noted that the power adjustment described at reference numeral 218 should not be confused with fast power control. Flow thereafter reverts back to the start.
• the base station If multiple transmissions occur in the same R-RACH slot, a collision occurs, and if the base station detects a preamble, it will start a power control bit stream corresponding to the R-RACH slot on which access was detected and power control the sum of the energies in the search window. If the base station fails to detect any preamble, it doesn't send a detection acknowledgment, and the colliding mobile stations abort transmission after a predetermined timeout.
• the base station may choose to transmit an abort message on the F-CACH and stop transmitting the F- PCCH sub-channel to any accessing mobile station if system parameters so dictate.

Landscapes

• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=23754492

Family Applications (1)

Country Status (3)

Cited By (2)

Citations (7)

• 2000
  • 2000-11-01 KR KR1020027006329A patent/KR20020058018A/ko not_active Application Discontinuation
  • 2000-11-01 AU AU15796/01A patent/AU1579601A/en not_active Abandoned
  • 2000-11-01 WO PCT/US2000/030079 patent/WO2001037455A1/en not_active Application Discontinuation

Patent Citations (7)

Also Published As

Similar Documents

Legal Events