EP0906673A4 - Systeme de communication sans fil a attribution dynamique de canaux - Google Patents

Systeme de communication sans fil a attribution dynamique de canaux

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Publication number
EP0906673A4
EP0906673A4 EP97917516A EP97917516A EP0906673A4 EP 0906673 A4 EP0906673 A4 EP 0906673A4 EP 97917516 A EP97917516 A EP 97917516A EP 97917516 A EP97917516 A EP 97917516A EP 0906673 A4 EP0906673 A4 EP 0906673A4
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EP
European Patent Office
Prior art keywords
channel
interference
cell
msc
base stations
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP97917516A
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German (de)
English (en)
Other versions
EP0906673A1 (fr
Inventor
John Plaschke
Jelena Vucetic
Paul A Kline
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Qorvo US Inc
Original Assignee
Watkins Johnson Co
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Publication date
Application filed by Watkins Johnson Co filed Critical Watkins Johnson Co
Publication of EP0906673A1 publication Critical patent/EP0906673A1/fr
Publication of EP0906673A4 publication Critical patent/EP0906673A4/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/02—Resource partitioning among network components, e.g. reuse partitioning
    • H04W16/10—Dynamic resource partitioning
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/16—Time-division multiplex systems in which the time allocation to individual channels within a transmission cycle is variable, e.g. to accommodate varying complexity of signals, to vary number of channels transmitted
    • H04J3/1605—Fixed allocated frame structures
    • H04J3/1623—Plesiochronous digital hierarchy [PDH]
    • H04J3/1629—Format building algorithm
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W28/00—Network traffic management; Network resource management
    • H04W28/16—Central resource management; Negotiation of resources or communication parameters, e.g. negotiating bandwidth or QoS [Quality of Service]

Definitions

  • the invention relates to a wireless communication system with dynamic channel allocation.
  • the invention provides the capability to dynamically allocate wireless communication channels to improve communication and reduce interference.
  • a traditional wireless communication system is constructed from a plurality of cells each having a base station. When the cells are configured in a mosaic-like pattern, wireless communication coverage area is achieved.
  • Traditional wireless communication systems employ various communication techniques on dedicated channels and spread spectrum channels. These various techniques include protocols such as TDM A, FDMA and CDMA. However, these techniques do not provide for the need to avoid interference among neighboring cells in a cellular network.
  • Some implementations dedicate various frequencies or hop sequences to distant cells in an attempt to avoid interference. While these implementations may work in some cases, they employ rigid rules that do not account for interference that may occur between some distant cells from time to time, and the lack of interference between other distant cells. That is, the rigid rules do not model the true communication environment and may either under compensate for interference or over compensate for interference.
  • the invention relates to a wireless communication system with dynamic channel allocation.
  • the invention provides the capability to dynamically allocate wireless communication channels to improve communication and reduce interference.
  • a plurality of base stations communicate with a plurality of mobile units.
  • Each base station includes a base station transceiver that receives inbound information from the mobile units and transmits outbound information to the mobile units.
  • a mobile switching center is coupled to the base stations and communicates the inbound information and outbound information with the base stations.
  • the base stations each include signal detectors that detect signal strength of the inbound signals, co-channel signals and adjacent channel signals. The MSC maintains a table of signal strength per communication channel and allocates communication channels to the base stations based on the signal strength information.
  • the inventive dynamic channel allocation system includes several channel allocation algorithms that can be active at the same time. Only one of the algorithms is active at any one time. The choice of the algorithm is based on current interference conditions and traffic load.
  • the invention is implemented in the MSC and base stations of a digital cellular network using wideband technology for its air interface. While the decision-making mechanism and the channel allocation algorithms are implemented in the MSC, the protocol between the MSC and base stations is extended to support the proposed concept for dynamic channel allocation.
  • the invention provides improvement in the overall network throughput for several reasons: a) the selection of channel allocation algorithm according to the interference and traffic load conditions; b) the utilization of wideband technology provides better selectivity of filters and improves channel reusability in the network. Advantages of the invention includes improved communication and reduced interference.
  • Figure 1 illustrates a two-dimensional model of a cellular network
  • Figure 2 illustrates a digital filter output compared to an analog filter output
  • Figure 3 illustrates a format for ANSI signaling connection control part messages
  • FIGS 4A-B illustrate two optional cell clusters according to embodiments of the invention
  • Figure 5 illustrates a mobile unit hand over from cell A to cell D
  • Figure 6 is a graph showing throughput versus offered load for different channel allocation algorithms with uniform load
  • Figure 7 is a graph showing throughput versus offered load for different channel allocation algorithms with non-uniform load
  • Figure 8 is a graph showing throughput versus offered load for varied configuration base stations with uniform load.
  • Figure 9 is a graph showing throughput versus offered load with update IT algorithm 1, and without update IT algorithm 2, updating interference information.
  • the invention relates to a wireless communication system with dynamic channel allocation.
  • the invention provides the capability to dynamically allocate wireless communication channels to improve communication and reduce interference.
  • the present specification describes how probability of blocking can be reduced using digital wideband technology, and a multi-algorithm dynamic channel allocation concept implemented in the MSC of a cellular network.
  • the invention addresses various design and implementation issues which are tightly related to dynamic channel allocation, and which are innovations compared to the already existing related solutions [And90, Eve89, Gam86, Nag87, Nan90, Tar88, Zha89b].
  • Section 2 A model of a cellular network is described in Section 2. Data structures that are used during dynamic channel allocation are defined in Section 3. Functions that can be executed using the data structures are described in Section 4. Section 5 provides definitions and measurements of co-channel and adjacent- channel interference. In Section 6, definitions and measurements of offered load are given. Section 7 describes a dynamic channel allocation concept and its implementation in a cellular network, assuming that interference constraints and offered load are dynamically updated. Both single- and multi-algorithm dynamic channel allocation concepts are discussed. Section 8 presents performance analysis of a network implementing the features described above. A conclusion is given in Section 9.
  • Cellular networks are usually modeled as sets of hexagonal cells which represent radio coverage areas [Jak74, Lee89, Par89].
  • Dimensions (x,y) of the network are X mtx and Y mxt respectively. Each cell is assigned a unique notation (x,y), where:
  • TT[x][y] A
  • Two cells are denoted in neighbors if there is a possibility of interference between them. We assume that interference between cells (X ⁇ ,Y ⁇ ) and (x 2 ,y 2 ) can be neglected if X ⁇ > X 2 _i_2, and/or y ⁇ >y 2 ⁇ . Under this assumption, each cell may have up to 19 neighbors: the cell itself, and the first and the second tier of cells around it.
  • DATA STRUCTURES The following data structures are implemented in the MSC to keep track of the network topology, interference conditions, and channel utilization. These information are used and updated by the channel allocation algorithms.
  • Update Interference Table When an Interference Update message from base station is received in the MSC, the IT table is updated with actual interference levels measured in base stations.
  • Allocate Radio Channel When a channel is allocated, its util sts in the UCT table becomes USED for the cell in which it is used. The all_sts of the channel in the ACT table becomes NOT_ALLOWED for all the cells that might suffer from co-channel interference. In addition, the all sts of adjacent channels changes to NOT_ALLOWED for all cells that might suffer from adjacent-channel interference. void Allocate_Channel(UWORD cell, UWORD channel)
  • ACT[neighbor][channel-l] ALLOWED
  • ACT[neighbor][channel+ l] ALLOWED
  • a spectrum reuse mechanism is used in cellular networks. It allows the same radio channels to be used simultaneously in different cells of the network as long as interference constraints are obeyed.
  • the constraints depend on propagation of radio signals in the network, which is a complex function of different time-variable parameters.
  • Co-channel and adjacent-channel interference are factors which may significantly deteriorate quality of transmission. They may appear in the receiver of a base station operating on any radio channel.
  • Co-channel interference may occur when two cells use the same channel simultaneously, and the signal in one cell is deteriorated by the signal from the other cell. To reduce this type of interference, the same channel should be used simultaneously in cells which are distant enough so that a sufficient level of carrier-to-interferer ratio is maintained.
  • Adjacent-channel interference appears when a signal is deteriorated by interference caused by signal(s) from adjacent radio channel(s).
  • Carrier to interference plus noise ratio C/(l+N) can be considered as a measure of co-channel plus adjacent channel interference in cellular networks.
  • a base station can measure C/(I+N) of a live mobile phone call in a non-interfering manner. To do so, one can measure the bit error rate and calculate C/(I+N).
  • an analog mode such as AMPS, a blank-and-burst acknowledgment on the reverse voice channel can be used to measure bit error rate [Str90].
  • E is the average energy per bit and ⁇ is the noise level per Hertz.
  • Q is defined as: Hence we can find E/ ⁇ .
  • Adjacent-channel interference is another factor that may reduce the quality of the radio signal.
  • One of the goals in the design of radio equipment is to achieve a high selectivity of radio signals, or, in other words, to minimize/reject all unwanted signals (such as signals in adjacent channels) in the receiver.
  • the dashed line in Figure 2 shows the AMPS standard selectivity specification.
  • the solid line is the selectivity using a sharp digital filter.
  • a digital receiver can easily achieve a filter loss of 70 dB at the adjacent channel using a 100 Tap FIR filter.
  • the path loss also attenuates an incoming adjacent channel signal.
  • the adjacent channel rejection at the base station receiver and transmitter is approximately 82 dB.
  • this type of adjacent channel rejection at the base station reuse of an adjacent channel at a neighboring cell is possible which in turn increases the throughput of the system.
  • Table 1 is a truth table to estimate the interference type (either none, co- channel only or both co-channel and adjacent channel).
  • Adjacent channel interference can be estimated by tuning a receiver to both of the adjacent channels and measuring their power.
  • ACI in Table 1 is calculated by adding the measured power from both adjacent channels and subtracting a constant which corresponds to the filter shape. For example if the adjacent channel to the left of the desired channel is -40 dBc and the right channel is -50 dBc.
  • the Threshold in Table 1 is defined as the maximum amount of interference allowed in the system, assuming that the call is maintained as a high quality call.
  • the MSC periodically updates information on interference conditions among network cells. This update is performed through a set of actions taken by the MSC and base stations.
  • the protocol of updating interference conditions is as follows: When the MSC wants to update these information, it sends a Measure Interference message to all base stations that are under its control.
  • the MSC starts its internal timer Int_Meas_Timer to control the time interval in which the MSC will collect Interference Update messages from all cells.
  • Each base station measures interference with neighboring cells, creates the response, and sends it back as an Interference Update message to the MSC.
  • the MSC updates the information on actual interference conditions in its memory. - When the MSC receives Interference Update messages from all cells in the network, or if Int Meas Timer expires, one cycle of the IT table updating is completed. In the first case, the MSC stops Int Meas Timer. The MSC continues to allocate radio channels to new calls using the updated information in the IT table. - The MSC supports the ongoing calls (originated before the update of constraints) using the already allocated radio channels, if it is possible. If the interference conditions do not allow a high-quality communication on the already allocated radio channels, the MSC should allocate new channels to the ongoing calls using the updated information on interference constraints, and release the channels used previously (intra-cell handoff).
  • Periodical update of interference conditions and constraints related to dynamic channel allocation is a new mechanism that can be added to the already existing standard functionalities of the MSC and base stations in cellular networks. This section describes how the already existing MSC and base stations can be expanded to enable this new system feature.
  • the MSC contains data structures defined in Section 4 in its global memory. These structures are periodically updated with actual measured interference conditions for each pair of network cells.
  • the MSC When the MSC wants to update interference conditions in the IT table, it sends a Measure Interference message to base stations. Base stations respond with Interference Update messages.
  • the Measure Interference and Interference Update messages can be treated as an extension of the standard A+ Interface between base stations and the MSC. The mechanism of their transmission is the same as of all other A+ Interface messages.
  • the MSC gets the received measured interference levels from base stations. Verifies that the received measurements are the most actual. Gets from the NT table the identities of all cells that are neighbors of cell A. - Compares if both cell A and each of its neighbors have determined the same level of interference (i.e. if IT[A][B] would be equal to IT[B][A] after the update), and updates the IT table accordingly. If there is a difference the higher of the two measured interference levels will be written in both ' IT[A][B] and IT[B][A]. - If the MSC has collected Interference Update messages from all cells, or if the Int Meas Timer timeout interval has expired, the MSC concludes that the update of the IT table has been completed for this cycle.
  • the function that executes periodical interference updates in MSC is called SC Update lnterference. Its pseudo-code is as follows: void MSC Update Interference ()
  • the TR-45 A-Interface protocol uses the Signaling Connection Control Part (ANSI-SCCP) of the Signaling System Number 7 (SS7) protocol as the transport layer. Both connectionless and connection-oriented services are utilized.
  • the Message Transfer Part (ANSI-MTP) of the SS7 protocol is also used as the underlying layer, giving service to the SCCP layer. Only a subset of the SCCP and MTP capabilities are needed.
  • the "Measure Interference" and "Interference Update” messages can be included into the standard set of Base Station Subsystem Management Application Part (BSSMAP) type messages. Their formats are shown in Figure 3.
  • the BSSMAP Header contains the following fields: Message Discriminator (1 byte); - Length indicator (1 byte).
  • the "Measure Interference" message does not contain any optional information elements.
  • the "Interference Update" message does not contain any optional information elements.
  • the new information element that should be included to the set of standard information elements is Measured Interference Levels. Its format is as follows: typedef struct ⁇ unsigned intjvl[19]:2; ⁇ INT LVL TYPE; INT_LVL_TYPE*Meas Interf_Lvl;
  • Each intjvl element of the INT LVL TYPE structure denotes a level of interference between the cell which measures the interference and each of its neighbors. Two cells are considered as neighbors if one of them belongs to either first or second tier of cells around the other. Each cell is considered as its own neighbor. Therefore, each cell has 19 neighbors: itself, 6 neighbors in the first tier, and 12 neighbors in the second tier.
  • the measured interference levels will be sorted in the INT LVL TYPE so that they correspond to the neighboring cells in the following order: 11, 12, 13, 17, 18, 19, 20, 23, 24, 25, 26, 27, 30, 31, 32, 33, 37, 38, and 39, respectively.
  • the order of interference levels in the INT LVL TYPE structure is very important because the order implicitly denotes the identity of the neighboring cell.
  • Each intjvl may have one of the following values: 0 (NOJNTERFERENCE), 1 (CO CHANNEL INTERFERENCE), or 2 (CO_ADJ ACENT_CH ANNEL INTERFERENCE) .
  • MSC performs the following actions:
  • MSC Verifies that the received Interference Measurement Reference Number information element correspond to the same type information element that has been most recently sent in the "Measure Interference" message to base station A. In other words, MSC verifies that the received measurements are the most actual.
  • MSC determines whether MSC has collected Interference Update messages from all cells, or if the timeout interval of Int_Meas_Timer has expired. If MSC has collected Interference Update messages from all cells, or if the timeout interval of Int_Meas_Timer has expired, MSC concludes that the update of the IT table has been completed for this cycle.
  • Each base station should contain a Partial Neighbor Table (PNT) in its global memory. This table contains information on all neighbors of the cell that is covered by this base station, in ascending order of their cell identities.
  • CO_ADJACENT_CHANNELJMTERFERENCE If co-channel interference is higher, and adjacent-channel interference is lower than the threshold, the corresponding measured interference level is set to CO_CHANNELJNTERFERENCE. If both co-channel and adjacent- channel interference are lower than the threshold, the corresponding measured interference level is set to NO INTERFERENCE.
  • Base station A creates an Interference Update message of all measured interference levels from its neighbors. - Base station A sends the Interference Update message to the MSC.
  • the channel allocation mechanism proposed in this paper takes into consideration fluctuations of the offered load and activates the algorithm which provides the best performance (among the available algorithms) for current load and its distribution over the network. Updating the information on current offered load requires additional activities in both MSC and base stations.
  • the MSC periodically sends a Measure Average Hourly Offered Load message to all base stations.
  • the MSC receives Offered Load Update messages from base stations.
  • the MSC determines if the load values have changed since the previous measurement, as well as if the load is uniform/non-uniform in the network. Based on these findings, the MSC decides if it is necessary to activate another channel allocation algorithm to improve performance. If another channel allocation algorithm should be activated, the MSC provides a smooth transition from the current to the new algorithm. During the transition, the MSC keeps information on currently active calls in order to prevent loss of communication among active mobile users due to the change of the algorithms.
  • Base station receives a Measure Average Hourly Offered Load message from the MSC.
  • each base station contains records of call attempts that enable statistical calculations of actual offered load.
  • Base station takes information on the number of call attempts in the previous time interval, and divides it by the length of the time interval. The ratio represents the actual offered load of the base station.
  • Base station sends the Offered Load Update message containing the actual offered load to the MSC.
  • DYNAMIC CHANNEL ALLOCATION Dynamic channel allocation is a mechanism that allows each channel from the cellular spectrum to be used in every cell. It should be implemented in both the MSC and base stations. Base stations should support the standard A + Interface protocol with several modifications/extensions. The decision-making on channel allocation, and keeping track on actual channel availability is moved from base stations to the MSC. So, instead of searching for an available channel in their own data structures, base stations should just receive the identity of an available channel from the MSC, and tune its corresponding components to the allocated channel. When a channel should be released, the base station deactivates these components, and sends a Release message to the MSC. The MSC changes the availability status of the channel, and allows it to be used for another calls.
  • Dynamic channel allocation has been proven [Cha86, Dim93, Eri88, Eve89, Sen80, Vuc92a, Yue91, Zha89b] to provide a considerably higher throughput than fixed channel allocation, which has been widely used in practice [Jak74, Lee89]. With new wideband base stations, dynamic channel allocation becomes a feasible and more attractive solution than fixed channel allocation.
  • a channel can be allocated to only one mobile user in a cell at a time
  • a channel cannot be used simultaneously in two cells if the corresponding interference level is CO ⁇ HANNEL INTERFERENCE or CO_ADJACENT_CHANNEL INTERFERENCE;
  • ACT[A][k] AVAILABLE, channel k is available for utilization in cell A. Otherwise, it should not be used.
  • Algorithm 1 The ACT is always searched in increasing order of channel indices k. The first available channel (the smallest k) is selected for allocation.
  • Algorithm 3 Each cell has its own subset of channels that may be allocated in this cell. The subsets are created obeying the interference constraints. Using digital filters, it is enough to provide four subsets (with already existing analog technology, it was necessary to provide seven subsets, which gives less channels per subset). Thus, the network is divided into exclusive four-cell clusters, as is shown in Figure 4. a. Each cluster of the network is assigned the whole cellular spectrum, i.e. a cluster represents a unit of spectrum reuse. When a new channel should be allocated, the first one (the smallest or the largest k) is selected from the ACT. There is no significant influence on the availability of other channels neither in the same nor in another cells. This is an improved version of the fixed channel allocation algorithm.
  • Each cell belongs to one and only one cluster of cells, which has one out of four subsets of channels.
  • Algorithm 4 The same as Algorithm 3, but applied to 7-cell clusters, as is shown in Figure 4.b. It represents a traditional fixed channel allocation, controlled and performed by base stations only, and using analog filters in the receivers. 7.1.2 CALL ORIGINATION CONTROL
  • the base station When there is a call origination request, the base station sends an A+ Interface standard Setup message to the MSC.
  • the MSC then activates its dynamic channel allocation procedure. Dynamic channel allocation during call origination in the MSC includes: searching for an available channel in the particular cell, reservation of the channel, and setting new constraints in interfering cells and channels. If there is an available channel, the MSC returns an Assignment Request message to the base station containing the channel identity. Upon receipt of the an Assignment Request message, the base station tunes its radio to the allocated channel, and establishes the voice channel with the mobile unit. If there is no available channel, the MSC should return a Release Complete message to the base station. Function Process Call Origination executes these activities. void Process Call Origination (WORD Cell)
  • Channel Find_Channel(Cell) ; if (Channel)! Allocate_Channel(Cell,Channel) ; Send_Assignment_Request(Cell, Channel) ;
  • the MSC When the MSC receives a Release message from a base station, it indicates that a call processed by the base station should be terminated. The MSC then activates its dynamic channel allocation procedure for call termination. It includes release of the voice channel that has been use din the call, and deleting the relevant constraints for interfering cells and channels. The MSC sends a Release Complete message to the base station. Function Process Call Termination executes these actions. void Process_Call_Termination (WORD Cell, WORD Channel)
  • the source base station When a call should be handed-off from one to another cell, the source base station sends an A+ Interface standard Handoff Required message to the MSC.
  • the MSC should then activate its dynamic channel allocation procedure for handoff. It includes searching for an available channel in the new cell, reservation of the new channel, release of the channel in the old cell that has been used in the call, and setting new constraints for interfering cells and channels for both old and new cell. If there is an available channel in the new (target) cell, the MSC returns a Handoff Command message to the old (source) base station, which indicates that the "old" channel will soon be released due to the handoff. The MSC also sends a
  • the MSC IF there is no available channel in the target cell, the MSC returns a Handoff
  • New_Channel Find_Channel (New Cell); if (New_Channel) ⁇ Allocate Hhannel (New_Cell, New_Channel); Release_Channel (Old_Cell, Old_Channel); Send_Handoff_Command (Old_Cell, Old Channel); Send JHandof ⁇ Request (New_Cell, New Channel);
  • a mobile unit is served by a cell as long as the signal quality is above a certain threshold.
  • the mobile When a mobile's signal quality goes under a certain threshold, the mobile is handed-over to an adjacent cell.
  • the mobile In the current system the mobile needs to retune its radio to one of the pre-assigned frequencies of the future hosting cell.
  • This type of handoff is called a hard handoff, which is noticeable by the user since the service is temporarily disrupted due to the retuning sequence. If a mobile is handed-over to another cell without retuning its radio, this is called a soft handoff. This type of handoff is "smooth" and does not disrupt the conversation.
  • the base station's radios are hardwired for fixed frequencies, however newer radios offer the capability to remotely tune to any portion of the cellular spectrum. With such radios, dynamic channel allocation and soft handoff are possible.
  • soft handoff is a natural extension. Shown in Figure 5, a mobile is entering cell D and departing from cell A. Since the signal quality at cell A becomes degraded, cell A notifies the MSC that a handoff needs to occur. The MSC gets measurements on signal quality from all of the neighboring cells and instructs the cell with the best signal quality, in this case cell D, to host the mobile. Cell D will allocate a radio resource to the mobile and (if possible) it will tune it to the frequency the mobile is currently tune to. Cell A will break its link with the mobile only after the MSC notifies it that cell D is actively hosting. This is a make-before-break type of contact.
  • This type of soft handoff cannot always occur. There are events where several mobile units tuned to the same frequency arrive at the same cell or at neighboring ceils.
  • the MSC performs spectral management. It must maintain sufficient frequency and spatial separation between mobiles. For instance, two mobiles in the same or neighboring cells must have at least one RF channel separation.
  • a multi-algorithm dynamic channel allocation mechanism consists of several channel allocation algorithms residing at the same time in the MSC of a cellular network.
  • the algorithms are selected so that each one of them provides a significant performance advantage in comparison to the others under the given traffic and interference conditions.
  • An algorithm becomes active in the network when the actual measured traffic and interference conditions indicate that this algorithm would provide the best performance in comparison to the other algorithms implemented in the MSC.
  • the algorithm becomes passive when the traffic and interference conditions change so that another algorithm is expected to provide a better performance. Only one of the available algorithms can be active in the network at a time.
  • the MSC In addition to the dynamic channel allocation activities described in Section 7.1, the MSC also executes the following activities while performing multi- algorithm dynamic channel allocation:
  • Transition from one to another algorithm should be smooth and efficient:
  • Each base station periodically measures actual offered load and interference conditions in its cell
  • Each base station periodically reports these measurements to the MSC;
  • the MSC compares all available channel allocation algorithms to determine which one provides the best performance (minimal blocking probability) under the most recently measured conditions;
  • the MSC determines if the algorithm transition is needed or the currently active algorithm is the best for the actual conditions; If the algorithm transition is not needed, the MSC continues operating with the actual algorithm until the next reports come from the base stations;
  • the MSC activates the new algorithm and turns off the old one; If the new algorithm requires a fixed, predetermined set of available channels in each cell, and the actual channel availability does not fulfill the requirement, the MSC orders the base stations that utilize inappropriate (for the new algorithm) channels at the moment, to perform an intra-cell handoff to the channels that are allowed by the new algorithm.
  • the MSC continues operating with the new algorithm, which gets as input parameters information on the actual channel availability, actual traffic and interference conditions, customers, and calls.
  • the multi-algorithm channel allocation mechanism provides a significant improvement in network performance (maximize throughput) because it selects the most superior available channel allocation algorithm with respect to the actual traffic and interference conditions.
  • this mechanism requires additional processing both in the MSC and in base stations, as well as an extension in the A+ Interface (additional messages or information elements within the already existing messages). It might reduce the efficiency of the system.
  • several software and hardware solutions have been considered [Vuc91, Vuc92b, Vuc93b].
  • Diagrams shown in Figure 6 illustrate throughput vs. offered load when each of the channel allocation algorithms described above is applied.
  • Algorithms 1, 2 and 3 have similar behavior, superior to Algorithm 4, as offered load is increased.
  • Better performance of the three first algorithms illustrate the advantages of utilization of wideband techniques and digital filtering (Algorithm 3) as well as of more intelligent decision making during channel allocation (Algorithms 1 and 2) compared to traditional fixed channel allocation concept (Algorithm 4).
  • Diagrams shown in Figure 8 illustrate throughput vs. offered load when the maximal number of radio channels per cell (configuration of base stations) is varied, applying Algorithm 1.
  • base stations can handle higher number of channels, throughput is higher.
  • the network reaches a saturation point. Additional channels per cell will not improve the performance because it is limited by another factor: the maximal number of available radio channels in the network (in our case, 333) combined with interference constraints.
  • This analysis may be useful for optimal network planning, where is important to achieve throughput as high as possible, while making minimal investments into the network equipment.
  • Diagrams shown in Figure 9 illustrate the improvement in performance when decision making during dynamic channel allocation is based on actual (periodically updated) information on interference conditions in the network, compared to the decision making which does not take into consideration the fact that interference conditions vary.
  • a part of the offered load will be dropped due to deteriorated interference conditions, while these calls were in progress.
  • the invention describes different advantages of dynamic channel allocation and digital filtering related to better performance of cellular networks.
  • Several new methods are proposed to increase the overall network throughput: Digital filters, which provide better selectivity, and therefore increase channel reusability in the network;
  • Periodical updating the information on interference conditions and offered load which are used during dynamic channel allocation. This enables better decision making because it is based on more accurate input data.
  • Advantages of the invention include improved computer system performance and reduced communication latency.

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

Abstract

Plusieurs stations de base sont en communication avec plusieurs unités mobiles. Chaque station de base inclut un poste émetteur-récepteur de base qui reçoit des unités mobiles l'information entrante et leur transmet l'information sortante. Un centre de commutation mobile (C.C.M.) relié aux stations de base reçoit et transmet l'information entrante ou sortante depuis ou vers les stations de base. Chaque station de base possède des récepteurs de signaux servant à mesurer l'intensité du signal de l'information entrante et à détecter l'information dans le même canal et dans le canal adjacent. Le C.C.M. dispose d'un tableau de puissance des signaux par canal de communication; l'attribution des canaux de communication aux stations de base se fait en fonction des informations sur la puissance du signal. Le procédé original d'attribution dynamique de canaux inclue un certain nombre d'algorithmes d'attribution de canal pouvant rester tous actifs en même temps. Un seul algorithme reste cependant actif à chaque moment donnée. Le choix de l'algorithme dépend des conditions d'interférence du moment et de l'intensité du trafic. L'invention s'utilise dans les stations de base et le C.C.M. d'un réseau de téléphones cellulaires en utilisant la technologie de large bande pour son interface de liaison sans fil.
EP97917516A 1996-03-08 1997-03-07 Systeme de communication sans fil a attribution dynamique de canaux Withdrawn EP0906673A4 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US1302096P 1996-03-08 1996-03-08
US13020 1996-03-08
PCT/US1997/003789 WO1997033394A1 (fr) 1996-03-08 1997-03-07 Systeme de communication sans fil a attribution dynamique de canaux
1997-12-18

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US6236656B1 (en) 1998-03-19 2001-05-22 Telefonaktiebolaget Lm Ericsson (Publ) Link-efficiency based scheduling in radio data communications systems
JP3334658B2 (ja) * 1999-01-07 2002-10-15 三菱マテリアル株式会社 無線通信処理装置およびその記録媒体
CN1242632C (zh) * 1999-02-16 2006-02-15 Ntt移动通信网株式会社 在移动通信系统中无线电信道分配判断方法和无线电信道控制装置
US6253083B1 (en) * 1999-07-21 2001-06-26 Lucent Technologies Inc. Mobile switching center for providing wireless access Ho
DE19941846C1 (de) * 1999-09-02 2000-11-23 Siemens Ag Verfahren zur Messung von Interzell-Interferenz in einem Frequenzkanal
EP1111843A3 (fr) * 1999-12-22 2003-03-26 AT&T Corp. Système et méthode pour coordonner de réseaux sans fil
FR2821230B1 (fr) * 2001-02-20 2003-04-11 Mitsubishi Electric Inf Tech Methode d'allocation de ressources de transmission

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EP0906673A1 (fr) 1999-04-07
AU2581097A (en) 1997-09-22

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