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WO2002037889A1 - Procede de selection de canal - Google Patents

Procede de selection de canal Download PDF

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Publication number
WO2002037889A1
WO2002037889A1 PCT/US2000/030283 US0030283W WO0237889A1 WO 2002037889 A1 WO2002037889 A1 WO 2002037889A1 US 0030283 W US0030283 W US 0030283W WO 0237889 A1 WO0237889 A1 WO 0237889A1
Authority
WO
WIPO (PCT)
Prior art keywords
carrier
carriers
power measurements
power
group
Prior art date
Application number
PCT/US2000/030283
Other languages
English (en)
Inventor
Rajaram Ramesh
Patrik Lundquist
Gunnar Rydnell
Original Assignee
Ericsson Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ericsson Inc. filed Critical Ericsson Inc.
Priority to AU2001213592A priority Critical patent/AU2001213592A1/en
Publication of WO2002037889A1 publication Critical patent/WO2002037889A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W48/00—Access restriction; Network selection; Access point selection
    • H04W48/20—Selecting an access point

Definitions

  • the present invention relates in general to mobile wireless communication systems, and more particularly, to a channel selection method for such systems.
  • EDGE Enhanced Data Rates for Global Evolution
  • GSM Global System for Mobile Communications
  • TIA Telecommunications Industry Association
  • EIA Electronic Industry Association
  • TDMA Time Division Multiple Access
  • EDGE Compact requires less than 1 MHz of spectrum for deployment while EDGE Classic requires 2.4 MHz of spectrum. In either case, when a mobile terminal is switched on, it is important for it to obtain service as soon as possible. For this to .
  • GSM 05.08 published by the European Telecommunications Standards Institute (ETSI), which deals with Radio Subsystem Link Control.
  • ETSI European Telecommunications Standards Institute
  • BCCH carriers carriers with broadcast and common control information
  • other carriers may have power variations and power off conditions at different times.
  • the channel selection procedure specified in GSM 05.08 requires the mobile terminal to do the following:
  • the present invention relates to a channel selection method implemented by a mobile terminal in a time division multiple access (TDMA) system.
  • TDMA time division multiple access
  • the mobile terminal attempts to find a channel on which to acquire service by performing a series of power measurements.
  • the mobile terminal performs a series of power measurements on the available carriers to find one or more control channels, and then selects a channel on which to acquire service.
  • EDGE Compact systems the control channel is not transmitted continuously so the method of performing power measurements needs to take the discontinuous transmission of control information into account .
  • the present invention provides a channel selection method particularly adapted for a system that transmits control information discontinuously.
  • the mobile terminal performs a plurality of power measurements on a plurality of carriers over a plurality of measurement periods on each carrier.
  • the measurement periods on each carrier are spaced at predetermined intervals of time and are interleaved with the measurement periods on other ones of the carriers in a manner to reduce the amount of time needed to select a channel.
  • the mobile terminal divides the available carriers into a plurality of groups of carriers. For each group, the mobile terminal performs power measurements on each carrier in sequence. The power measurements are repeated a predetermined number of times on each carrier. More particularly, the mobile terminal selects a carrier, performs power measurements over a predetermined measurement period, stores the highest value obtained during the measurement period, and then changes to the next carrier in the group. The mobile terminal repeats this process for each carrier within the group to complete one measurement cycle. The measurement cycle is then repeated until a predetermined number of valid power measurements are obtained for each carrier in the group.
  • the mobile terminal After performing the power measurements as described above, the mobile terminal averages the five highest power measurements for each carrier to obtain an average power for each carrier. The mobile terminal then selects a plurality of candidate carriers by choosing those with the highest average power. Once the candidate carriers are identified, the mobile terminal selects one of the candidate carriers on which to acquire service, synchronizes to the selected channel, reads the information on the broadcast control channel, and then registers with the network.
  • Figure 1 is a network diagram illustrating an exemplary wireless communications system.
  • Figure 2 is a cell plan for the exemplary wireless communications system of Figure 1.
  • Figure 3 is a diagram illustrating the frame structure used by the exemplary wireless communications system of Figure 1.
  • Figures 4A-4D are diagrams illustrating the frequency and time reuse plan implemented by the exemplary wireless communications system of Figure 1.
  • Figures 5A-5C are diagrams illustrating how the power measurements in one illustrative embodiment are interleaved.
  • Figure 6 is a block diagram of an exemplary mobile terminal that implements the channel selection method of the present invention.
  • Figure T a flow chart illustrating the channel selection procedure according to the present invention.
  • the wireless communications system 10 implements the Global System for Mobile Communications (GSM) standard published by the European Telecommunications Standards Institute (ETSI). More particularly, the wireless communications system 10 implements the variant of GSM known as Enhanced Data Rates for Global Evolution (EDGE) Compact. Those skilled in the art will appreciate, however, that the present invention may be used for other types of wireless communication systems and access protocols, such as the Telecommunications Industry Association/ Electronics Industry Association (TIA/EIA) standard TIA/EIA-136.
  • GSM Global System for Mobile Communications
  • ETSI European Telecommunications Standards Institute
  • EDGE Enhanced Data Rates for Global Evolution
  • Each base station 12 is located in and provides services to a geographic region referred to as a cell. In general, there is one base station 12 for each cell within a given wireless communications system 10. Within each cell, there may be a plurality of mobile terminals 100 that communicate via radio link with the serving base station 12.
  • Base stations 12 connect via one or more MSCs 14 to external wireline networks 18 such as the Public Switched Telephone Network (PSTN), the Integrated Services Digital Network (ISDN), and/or the Internet.
  • PSTN Public Switched Telephone Network
  • ISDN Integrated Services Digital Network
  • At least one MSC 14 may serve as a gateway to the external wireline network 18 or to other Public Land Mobile Networks (PLMNs).
  • PLMNs Public Land Mobile Networks
  • FIG 2 is a cell plan for the wireless communications system 10 implementing the EDGE Compact standard which employs time and frequency reuse.
  • Each cell comprises three sectors (represented as hexagons in Figure 2), which are typically served by a single base station 12.
  • Each base station 12 is allocated at least three carrier frequency groups; one for each sector.
  • the carrier frequency groups are reused in each sector using a 1/3 frequency reuse pattern as shown in Figure 2.
  • the carrier frequency groups may comprise one or more carrier frequencies.
  • Each carrier frequency is subdivided into frames, and each frame is further subdivided into eight time slots, as shown in Figure 3.
  • the frames are approximately 4.6 ms in length.
  • the time slots are approximately .577 s in length.
  • Selected time slots in selected frames are used as control channels to transmit and receive packet control signaling while the remaining time slots serve as traffic channels to transmit and receive user data, i.e., voice or packet data.
  • Base station timing for all bases stations 12 is synchronized so that all base stations 12 use the same frame and hyper-frame timing. Inter base station synchronization makes it possible to create time groups. Time groups are used to create a time reuse pattern on top of the frequency reuse pattern to create a higher effective reuse for certain control channels. Time groups are not typically employed for traffic channels.
  • time groups are defined but one may chose not to use all of them.
  • Each sector is assigned to one time group.
  • the time groups are arranged in a 1/4 reuse pattern, as shown in Figure 2. To avoid adjacent ' channel interference, adjacent sectors are assigned to different time groups.
  • time group 1 may use slot 1 for packet control signaling
  • time group 2 may use slot 3
  • time group 3 may use slot 5
  • time group 4 may use slot 7.
  • the sectors belonging to the other time groups are idle, i.e. are silent on both the uplink and downlink.
  • the superimposition of the time reuse pattern on top of the frequency reuse pattern creates a higher effective reuse pattern for packet control signaling.
  • FIGS 4A-4D illustrates the EDGE Compact Frame Structure, which is used in the exemplary embodiment described herein.
  • the frame structure is based on a matrix with 52 rows and 8 columns, where columns represent time slots and rows represent succeeding frames in a 52-frame multiframe.
  • Time slot mapping is carried out such that broadcast channel (BCCH), common control channel (CCCH), Frequency Correction Channel (FCCH), and Synchronization Channel (SCH) of a certain time group rotate their time slot position over odd-numbered time slots. Only the FCCH, SCH, BCCH and CCCH rotate their time slot position from one multiframe to the next. The traffic channels do not rotate their time slot position. The rotation occurs once a multiframe between frames 4 and 5.
  • BCCH broadcast channel
  • CCCH common control channel
  • FCCH Frequency Correction Channel
  • SCH Synchronization Channel
  • the pattern of rotation will therefore repeat itself every four multiframes creating a 208 multiframe pattern. If the sequence number of a 52-frame multiframe is denoted as N, then the four different rotation possibilities (0,1,2, and 3) is given as N MOD 4.
  • the rotation patterns for all four time groups are offset so that at any given time each time group employs a different rotation as shown in Figure 4. Thus, in blocks where time group 1 is transmitting packet control signaling, time groups 2, 3 and 4 are idle. Similarly, in blocks where time group 2 is transmitting packet control signaling, time groups 1 , 3 and 4 are idle; in blocks where time group 3 is transmitting packet control signaling, time groups 1 , 2 and 4 are idle; and in blocks where time group 4 is transmitting packet control signaling, time groups 1, 2 and 3 are idle.
  • time group 1 transmits the BCCH in time slot 1 during rotation
  • Time group 2 transmits the BCCH during time slot 3
  • time group 3 transmits the BCCH during time slot 5
  • time group 4 transmits the BCCH during time slot 7.
  • each time group shifts its transmit slot two slots right so that time group 1 transmits the BCCH on time slot 3.
  • Time groups 2 and 3 likewise shift right by two time slots.
  • Time group 4 rotates circularly from time slot 7 to time slot 1. This rotation occurs each multiframe and repeats every four multiframes.
  • carriers with broadcast and control channel information are broadcast continuously with constant power.
  • the mobile terminal 100 can locate a control channel by performing power measurements on the available carriers and selecting as candidates those with the highest power levels.
  • packet control signaling is not transmitted continuously. Instead, packet control signaling is transmitted in selected time slots on carriers that also carry traffic. While certain control channels are transmitted at constant power, which is typically maximum power, the power level on the traffic channel is constantly varying.
  • the control channels transmitted at constant power are referred to herein as power reference channels.
  • the power reference channels in the exemplary embodiment comprise the BCCH, CCCH, SCH, or FCCH.
  • the discontinuous transmission of packet control signaling makes power measurement during a power-up more difficult. If a power measurement is made over a short period of time, for example a few frames, there is no guarantee that the measurement would be at a time when the base station is transmitting at maximum power (i.e., during a BCCH, CCCH, SCH, or FCCH).
  • the mobile terminal 100 could perform a series of power measurements over a period of about twenty frames, in which case the mobile terminal 100 would be assured of obtaining at least one valid power measurement of a power reference channel. This method, however, would require a relatively long period of time to complete, particularly if there are a large number of available channels.
  • the present invention provides a method of performing power measurements in a more time efficient manner so that the mobile terminal 100 can select a channel and acquire service with the wireless communications system 10 more quickly.
  • the mobile terminal 100 performs power measurements on each carrier in one or more frequency bands of interest.
  • the mobile terminal 100 divides the total number of carriers, denoted as N t , into groups of N c carriers. Note that the number of carriers in a group need not divide evenly into the total number of carriers. Some or all groups may use dummy carriers if that group has less than N c carriers. Alternatively, some carriers may be included in more than one group to ensure that each group has N c carriers. Moreover, all carriers could be assigned to a single group.
  • the mobile terminal 100 performs a sequence of power measurements in a manner described below to ensure that a predetermined number of valid power measurements are obtained for each carrier.
  • a valid power measurement is one which is obtained while a power reference channel (e.g., BCCH, CCCH) is being transmitted.
  • the mobile terminal 100 averages a selected number of the power measurements with the highest values to obtain an average maximum power value for each carrier frequency.
  • a selected number of the carrier frequencies are selected as candidate carriers. The selected carriers are those with the highest average maximum power value.
  • the mobile terminal 100 of the present invention interleaves the power measurements on a plurality of carriers in a manner to lessen the time needed to complete the power measurements. Instead of making continuous power measurements on each frequency for a sufficient time to ensure one valid measurement, the mobile terminal 100 of the present invention performs measurements over a plurality of time intervals which are spaced from one another. More particularly, the mobile terminal 100 will lock on and perform multiple power measurements in a fixed interval of time, referred to herein as the measurement period T m , on each carrier. The maximum of these power measurements taken over the measurement period T m is stored. This process is repeated for each carrier frequency within the carrier group to complete one cycle.
  • the mobile terminal 100 After going through all N c carriers in the group, i.e., one cycle, the mobile terminal 100 returns to the first carrier and repeats the power measurements for each carrier in the group. The mobile terminal 100 repeats the power measurements on each carrier a predetermined number of times to ensure at least five valid power measurements.
  • the number of carriers in each group N c , the measurement period T m , and the number of repetitions k on each carrier are chosen to minimize the time needed to obtain the desired number of valid power measurements.
  • Figures 5A-5C illustrate one example of the channel selection method according to the present invention.
  • the example in Figures 5A-5C is suitable for use in the EDGE Compact system of Figures 1 and 2.
  • EDGE Compact employs three carrier frequencies.
  • the total number of available carriers, N t is three.
  • N c is also equal to three.
  • Figures 5A-5C show a multiframe for each of the three carrier frequencies.
  • the shaded time slots in Figures 5A-5C represent the measurements periods T m during which power measurements are taken on each carrier.
  • the measurement period T m is equal to nine time slots.
  • One time slot is needed for the frequency synthesizer to settle on the desired frequency so that power measurements are actually taken over eight time slots.
  • the spacing between measurement periods in this example is (N c -1)x9 which equals eighteen time slots.
  • the present invention significantly reduces the time needed to obtain the desired number (in this case, the desired number is 5) of power measurements.
  • N t the total number of carrier frequencies N t is equal to 967.
  • T m the measurement period
  • N c the number of carriers per group
  • N 0 eighteen measurement periods for each carrier frequency are needed to ensure five valid power measurements.
  • N c the total measurement time to obtain five valid power measurements was found to be 90.37 seconds.
  • N 0 When the value of N 0 is large, as in the last example, consecutive power measurements on the same carrier will not occur in the same frame. However, consecutive measurement periods will occur at different locations in the multiframe. The spacing between measurement periods depends on the number of carriers within a group N c , and the length of the measurement period T m , which can be chosen to minimize the time needed to acquire the measurements. Values for N c and the measurement period T m can be determined by means of a computer simulation which computes the total measurement time based on different values of N c and T m .
  • FIG. 6 is a block diagram of an exemplary typical mobile terminal 100 that implements the channel selection method of the present invention.
  • the term mobile terminal 100 means any device capable of wireless communications.
  • a mobile terminal 100 may, for example comprise a cellular radiotelephone, a personal communications terminal that combines a cellular radiotelephone with data processing capabilities, such as a Personal Communication System (PCS) device or Personal Digital Assistant (PDA), or a portable computing device, such as laptop computer or palmtop computer, equipped with a radiotelephone.
  • PCS Personal Communication System
  • PDA Personal Digital Assistant
  • Mobile terminals 100 may also be referred to as "pervasive computing" devices.
  • the mobile terminal 100 includes a main control unit 102 for controlling the operation of the mobile terminal 100 and a memory 104 for storing control programs and data used by the mobile terminal 100 during operation.
  • Input/output circuits 106 interface the main control unit 102 with a keypad 108 or other user input device, display 110, audio processing circuits 112, receiver 120, and transmitter 122.
  • the keypad 108 allows the operator to dial numbers, enter commands, and select options.
  • the display 110 allows the operator to see dialed digits, stored information, and call status information.
  • the audio processing circuits 112 provide basic analog audio outputs to a speaker 114 and accept analog audio inputs from a microphone 116.
  • the receiver 120 and transmitter 122 receive and transmit signals using shared antenna 124.
  • Digital signal processing (DSP) circuits 126 process signals transmitted and received by the mobile terminal 100.
  • the DSP circuits 126 include power measurement circuits to determine the power of signals received by the mobile terminal 100.
  • the mobile terminal 100 may further comprise a GPS receiver 130 or other type of positioning receiver.
  • the GPS receiver 130 enables the mobile terminal 100 to determine its current location based on positioning signals transmitted by a GPS satellite.
  • the GPS receiver 130 includes a separate antenna 132, however, the GPS receiver 130, the receiver 120, and transmitter 122 could use a shared antenna.
  • the main control unit 102 implements the communication protocols used by the mobile terminal 100.
  • the communication protocol specifies timing, multiple access approach, modulation format, frame structure, power level, as well as many other aspects of mobile terminal operation.
  • the main control unit 102 inserts signaling messages into the transmitted signals and extracts signaling messages from the received signals.
  • Main control unit 102 acts on signaling messages received from the base station 12 as set forth in the communication protocol.
  • Figure 7 is a flow chart illustrating an exemplary channel selection procedure according to the present invention implemented by the main control unit 102.
  • the channel selection procedure of Figure 7 begins when the mobile terminal 100 is powered on (block 200).
  • the purpose of the channel selection procedure is to enable the mobile terminal to locate a channel on which to acquire service.
  • the mobile terminal 100 divides the available carriers into groups of N c carriers per group (block 202).
  • the mobile terminal 100 selects a first group of carriers (block 204) and a first carrier in the selected group (block 206) to begin performing power measurements.
  • the mobile terminal 100 measures power on the selected carrier beginning with the first carrier in the selected group.
  • the power measurement is performed over a predetermined interval of time T m , which in the exemplary embodiment is equal to nine time slots (which includes the time needed to switch to the carrier).
  • a plurality of time measurements are made during the measurement period T m and the highest measurement obtained during the measurement period T m is stored (block 210).
  • the mobile terminal 100 determines whether it has reached the last carrier in the group (block 212). If not, the mobile terminal 100 switches to the next carrier in the group (block 214) and performs power measurements on the newly selected carrier (block 208). This process repeats until the last carrier in the group is reached. Once the last carrier in the group is reached, the mobile terminal 100 determines whether the specified number of repetitions has been completed (block 216).
  • the mobile terminal 100 returns to the first carrier in the group (block 218) and repeats the power measurements on each carrier.
  • Decision block 216 ensures that the mobile terminal 100 repeats the power measurements on each carrier in the group a predetermined number of times. The number of repetitions is chosen to ensure at least five (or some other specified number) valid power measurements of a power reference channel on each carrier.
  • the mobile terminal 100 determines whether the currently-selected group is the last group (block 220). If not, the mobile terminal 100 selects the next group of carriers (block 222). The mobile terminal 100 selects an initial carrier in the newly selected group (block 206) and begins performing power measurements (block 208). The mobile terminal 100 repeats the power measurements (block 208) on each carrier in the newly selected group until the final carrier in the final group is reached.
  • the mobile terminal 100 then averages a specified number (e.g., five) of the highest power measurements for each carrier to obtain an average power for each carrier (block 224). This is done for the purpose of alleviating Rayleigh fading effects, which are common in radio channels. By averaging power values spaced in time, the fading effects are averaged out.
  • the mobile terminal 100 selects one or more candidate carriers (block 226) based on the average power of the carriers.
  • the mobile terminal 100 selects one carrier from among the candidate carriers on which to acquire service (block 228).
  • the details of how the final selection is made are well known in the art and are not material to the present invention.
  • the final selection criteria is typically dependent upon the particular service provider. In general, the service provider programs the mobile terminal 100 to select those carriers which it most prefers from among the available candidate carriers. If one of the carriers is the home carrier for the mobile terminal 100, that carrier will typically be selected provided that quality of service requirements are met. The remaining carriers are divided into classes based on the preference of the service provider.
  • the mobile terminal 100 attempts to acquire service on the carrier.
  • the mobile terminal 100 typically locks on to the Frequency Correction Channel (FCH) to obtain coarse information about timing and frequency offset. It then locks on the Synchronization Channel (SCH), which occurs at a fixed time offset away from the FCH, and obtains information regarding the position of the BCCH. It then reads the BCCH and is ready to register to the system. After registering, the mobile terminal 100 enters the camping state on the selected control channel.
  • the channel selection procedure terminates when the mobile terminal enters the camping state on a selected carrier (block 230).

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

Abstract

L'invention concerne un procédé de sélection de canal mis en oeuvre par un terminal mobile dans un système d'accès multiple à répartition dans le temps. Le terminal mobile effectue plusieurs mesures de puissance sur plusieurs porteuses sur plusieurs périodes de mesure sur chaque porteuse. Les périodes de mesure sur chaque porteuse sont espacées à des intervalles de temps prédéterminés et sont entrelacées par des périodes de mesure sur d'autres porteuses. Le terminal mobile sélectionne un canal en fonction des mesures de puissance.
PCT/US2000/030283 2000-11-01 2000-11-02 Procede de selection de canal WO2002037889A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001213592A AU2001213592A1 (en) 2000-11-01 2000-11-02 Channel selection method

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US70416300A 2000-11-01 2000-11-01
US09/704,163 2000-11-01

Publications (1)

Publication Number Publication Date
WO2002037889A1 true WO2002037889A1 (fr) 2002-05-10

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1422961A1 (fr) * 2002-11-19 2004-05-26 Nec Corporation Procédé et dispositif d'acquisition de réseau cellulaire
EP2219406A1 (fr) * 2009-02-11 2010-08-18 Motorola, Inc. Sélection de station de base pour un système de communication sans fil

Citations (2)

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Publication number Priority date Publication date Assignee Title
EP0468569A2 (fr) * 1990-07-23 1992-01-29 Philips Electronics Uk Limited Procédé pour exploiter un système de communications, système de communications et station secondaire pour utilisation dans le système
EP0877510A2 (fr) * 1997-05-07 1998-11-11 Nokia Mobile Phones Ltd. Mesure de cellules voisinés dans un réseau cellulaire AMRT

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0468569A2 (fr) * 1990-07-23 1992-01-29 Philips Electronics Uk Limited Procédé pour exploiter un système de communications, système de communications et station secondaire pour utilisation dans le système
EP0877510A2 (fr) * 1997-05-07 1998-11-11 Nokia Mobile Phones Ltd. Mesure de cellules voisinés dans un réseau cellulaire AMRT

Non-Patent Citations (1)

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Title
PIRHONEN R ET AL: "TDMA BASED PACKET DATA SYSTEM STANDARD AND DEPLOYMENT", HOUSTON, TX, MAY 16 - 20, 1999,NEW YORK, NY: IEEE,US, vol. CONF. 49, 16 May 1999 (1999-05-16), pages 743 - 747, XP000941454, ISBN: 0-7803-5566-0 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1422961A1 (fr) * 2002-11-19 2004-05-26 Nec Corporation Procédé et dispositif d'acquisition de réseau cellulaire
GB2395622B (en) * 2002-11-19 2004-09-29 Nec Technologies Cellular network acquisition method and apparatus
US7620395B2 (en) 2002-11-19 2009-11-17 Nec Corporation Cellular network acquisition method and apparatus
EP2219406A1 (fr) * 2009-02-11 2010-08-18 Motorola, Inc. Sélection de station de base pour un système de communication sans fil

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