MXPA98010062A - Method and device for dynamic assignment of resources for broadband services in a wireless communication system - Google Patents

Abstract

A method and apparatus for dynamic allocation of resources for broadband services in a wireless communications system is provided. The communications system can have numerous cells, each of which has multiple sectors. Each sector can contain several communication sites. The information is transmitted in programmed time sub-frames to avoid interference between the sectors and cells, and different degrees of concurrent packet transmission can be programmed for different classes of communication sites. The communication sites can be classified on the basis of reception quality, for example by comparing their measured signal to interference ratio (SIR) with a threshold S

Description

METHOD AND APPARATUS OF DYNAMIC ALLOCATION OF RESOURCES FOR BROADBAND SERVICES IN A WIRELESS SYSTEM OF COMMUNICATIONS FIELD OF THE INVENTION The invention relates to wireless communications systems. More particularly, the invention relates to a method and apparatus for dynamic allocation of resources for broadband services in a wireless communication system.

ANI? 'CKUENTES OF THE INVENTION The need for high-speed broadband package services will grow tremendously as telecommunication and Internet access become increasingly popular. Customers will expect high quality, reliable access to high-speed communications for homes and small businesses in order, for example, to have access to: (a) the world wide web for information and entertainment; (b) office equipment and data from the houses at speeds comparable to local area networks (LAN); and (c) multimedia services such as voice. image and video. Although they vary with the application, effective broadband communication requires sufficient bandwidth to allow the speed of the data to increase to the range of several tenths of megabits per second (Mbps). Traditional wireless communication systems have a problem in providing high-speed services due to the amount of bandwidth these services require. Bandwidth is a key bidding factor to determine the amount of information a system can transmit to a user at any time. In terms of wireless networks, the bandwidth refers to the difference between the two limiting frequencies of a band, expressed in Hertz (Hz). The concept of bandwidth can be better understood using an analogy. If the information conveyed by a network were water, and the links between the communication sites were pipes, the amount of water (ie, information) that a network could transmit from one site to another would be limited by the speed of the water and the diameter of the tubes that transport the water. The larger the diameter of the tube, the more water (ie, more information) can be transmitted from one site to another in a given time interval. Similarly, • the more bandwidth a communication system has available, the more information it can carry.

Traditional wired communications systems using modems and a physical transmission medium such as a twisted-pair copper wire can not currently achieve the data rates needed to provide a high-speed service due to bandwidth limitations ( that is, small tubes). The promising technologies of wired networks for broadband access such as the asymmetric digital subscriber circuit (ADSL) and hybrid coaxial fiber (HFC), can be expensive and require time to install. The benefit of wireless systems for providing high-speed service is that they can be rapidly developed without installation of local wire-mesh distribution networks. However, traditional wireless systems such as narrowband cellular services and personal communications services (PCS) are limited in bandwidth. As an alternative, wireless solutions such as the multi-channel multi-point distribution service (MMDS) and the local multiple-channel distribution service (LMDS) have become attractive, but these solutions currently offer a limited capacity to increase Channel links and may not be able to support a lot of users.

One solution to solve the problem of limiting bandwidth for wireless systems is to maximize the available bandwidth by reusing frequency. Frequency reuse refers to reusing a common frequency band in different cells within the system. With reference, for example, to figure 1, which shows a typical wireless communication system. A base station (BS) 20 communicates with several terminal stations (TS) 22. The BS 20 is usually connected to a fixed network 24, such as the public switched telephone network (PSTN) or the internet. The BS 20 can also be connected to other base stations, or to a mobile telephone switching office (MTSO) in the case of a mobile system. Each TS 22 can be fixed or mobile. The BS 20 communicates information to each TS 22 using radio signals transmitted over a range of carrier frequencies. The frequencies represent a finite natural resource and are of extremely high demand. In addition, frequencies are heavily regulated by federal and state governments. As a result, cellular systems have access to a very limited number of frequencies. As a result, wireless systems try to reuse frequencies in as many geographic areas as possible. To do this, a cellular system uses a frequency reuse pattern. A major factor in designing a frequency reuse pattern is to try to maximize system capacity while maintaining an acceptable ratio of signal to interference (SIR). The SIR refers to the proportion of the desired signal level received relative to the level of the unwanted signal received. Co-channel interference is interference due to the common use of the same frequency band by two different cells. To determine frequency reuse, a cellular system takes the total frequency spectrum assigned to the system and divides it into a set of smaller frequency bands. Cellular communication systems have numerous communication sites placed through a geographic coverage area served by the system. The geographical area is organized into cells and / or sectors, where each cell typically cins a plurality of communicators, sites such as a base station and terminal stations. A cell can have any of many shapes, such as a hexagon. Groups of cells can be formed, where each cell in the group uses a different frequency band. The groups are repeated to cover the entire service area. Therefore, in essence, the frequency reuse pattern represents the geographical distance between cells using the same frequency bands. The objective of a frequency reuse pattern is to keep the co-channel interference below a given threshold and to ensure a successful signal reception. The most dynamic frequency reuse pattern is that where the same frequency band is used in each cell. An example of such a system is code division multiple access (CDMA) systems, which broadcast the signal transmitted over a wide frequency band using a code. The same code is used to recover the signal transmitted by the CDMA receiver. Although CDMA systems reuse the same frequencies from cell to cell, they require a large amount of frequency spectrum. In fact, the amount of spectrum required by CDMA systems to provide high-speed broadband services to a large number of users is commercially unrealistic. Another example of dynamic frequency reuse is time division multiple access (TDMA) systems, an example of which is discussed in U.S. Patent Number 5,355,367, which uses redundant transmission of information packets to secure an SIR adequate The use of redundant packet transmissions, however, only transfers one inefficiency for another. Although a frequency band can be reused from one cell to another, the transmission of redundant packets means that a smaller portion of the frequency band now available for use by each cell in the system, since multiple packets are required to ensure the useful reception of a single packet. In addition to the problem of frequency reuse, traditional cellular systems are not designed to allow a communications site to use all of the available bandwidth for the system (or "total systems bandwidth"). Instead, traditional cellular systems use various techniques in both the frequency domain and the time domain to maximize the number of users able to be served by the system. These techniques are predicated to allocate smaller portions of the total system bandwidth to serve individual communication sites. These smaller portions are unable to provide enough bandwidth to offer high-speed services. An example of a technique used in the frequency domain is frequency division multiple access (FDMA). FDMA is divided into available bandwidth into smaller sections of bandwidth under the concept of providing less bandwidth for a larger number of users. Using the water / tube analogy, a single large tube is separated into several smaller tubes, each of which is assigned to a sector or cell. Unfortunately, the smaller frequency bands are too small to support the high-speed broadband packet services. Furthermore, by definition, a communication site is not capable of using the total bandwidth of the system, but rather is limited to a discrete portion of the total system bandwidth. An example of a technique used in the time domain is TDMA described above. Using the water / tube analogy, each cell or sector has access to the entire tube for a fixed amount of time. These systems assign a specific time interval of a fixed duration for a specific communication site. As a result, a communication site can not transmit more information than it can accommodate for its allocated time slot. Traditional TDMA systems are designed to handle circuit switching and, therefore, are static in nature. Therefore, traditional TDMA systems are not designed to take advantage of new switching technology, such as packet switching. Some systems use a combination of FDMA and TDMA to improve the call capacity of the system. However, FDMA / TDMA systems only combine the disadvantages of both and do not allow a user access to the total system bandwidth on a dynamic basis. To solve this problem, some systems use a concept called "dynamic allocation of resources" to share the radio resource between communication sites in an efficient manner, however, dynamic resource allocation methods require a central controller or complicated algorithms. to determine dynamically the available time intervals and coordinate their use by communication sites In order to increase spectrum efficiency, other cellular systems have used multiple frequency reuse patterns within the same system. United States Number 4,144,411 issued to Frenkiel on March 13, 1979, describes the static reuse of frequencies in a system that uses a miniature size overlay in each cell, with the miniature size overlay using the same type of reuse pattern as the cell reuse pattern This is obtained through even lower transmission energies and maintain the same separation of site at the radius of the cell as the large cell. This concept is typically referred to as a cell division. An improvement to Frenkiel is discussed in an article whose author is Samuel W. Halpern entitled Reuse Partitioning in Cellular Systems, presented at the 33rd IEEE Vehicular Technology Conference on May 25-27, 1983 in Toronto, Ontario, Canada. Halpern's article establishes a cellular system that has multiple frequency reuse levels (or patterns) within a given geographic area. For example, a group of cells that normally use a seven-cell reuse pattern simultaneously can operate in a three-cell reuse pattern and a nine-cell reuse pattern. One set of frequencies is dedicated to the three-cell reuse pattern while another set of frequencies is dedicated to the nine-cell reuse pattern. Generally, the principle behind the Halpern system is to allow a degradation of the carrier performance with respect to interference (C / I) for those subscriber units that already have more than adequate C / I protection and at the same time provide greater C / I protection. I to those subscribers who require it. Therefore, a subscriber with the best received signal quality will be assigned a set of channels for the three-cell reuse pattern while being able to tolerate more co-channel interference than a subscriber whose signal quality is poorer. The subscriber that has the poorest received signal quality is therefore assigned to a channel corresponding to the nine cell reuse pattern. The Halpern system, like the previous multiple frequency reuse division systems, is unsatisfactory for numerous reasons. For example, in practice, the Halpern system allows only a small fraction of total traffic to use the closest reuse pattern for the miniature size overlay, leaving little or no gain in system capacity. In addition, the Halpern system is designed for circuit switched systems, and not for modern packet switched systems. More specifically, circuit switched systems can tolerate a large amount of measurement overload and delay when connected to the user. If the same technique is applied to a packet switched system, however, several measurements would be required before transmitting each packet. The overload and delay introduced would be excessive, and therefore the method described in the Halpern reference would not be feasible. In fact, the Halpern method is designed for the conventional telephone system and not for packet switched systems in general. In addition, the previous systems were designed to perform the reuse division in the frequency domain, and this is where the division of the total frequency bandwidth available for the system and the assignment of a portion of this frequency bandwidth is focused. total to a reuse pattern and another portion to another reuse pattern. However, dividing the available frequency limits the maximum speed of data that can be provided by any single user or application by the system. Therefore, frequency reuse division schemes are not suitable for supporting high-speed data applications such as those considered for broadband wireless systems. A specific implementation of the frequency reuse division is described in U.S. Patent No. 5,038,399 (the "Bruckert patent"). The Bruckert system is directed towards a mechanism to measure the various signal strengths from the base stations in the subscriber stations through the system, constructing a gradient of reuse level, and this gradient is used as a basis to switch between patterns of multiple frequency reuse. As with the Halpern system, the Bruckert system is unsatisfactory for numerous reasons. For example, the Bruckert patent is also directed towards circuit switched systems and is not designed for modern packet switched systems. As a result, the bandwidth available to a user is fixed for the duration of the call, and becomes inflexible to handle data downloads as anticipated in broadband services. In addition, the Bruckert patent describes a method for assigning different users to different levels of reuse according to the "reuse level gradient" which is another way of establishing the assignment based on different interference levels. In many cases, however, an integrated system that provides different services to the same user may require different levels of reuse due to different service requirements, even if it experiences the same interference. The Bruckert patent does not describe the way in which the quality of service is maintained (QoS) for each application using this method. In addition, the Bruckert patent does not describe any technique for ensuring cleanliness between communication sites in terms of each site having access to the communication resource in a uniform manner. Finally, the Bruckert patent does not describe the use of multiple reuse patterns in the time domain, as in the systems previously discussed. In view of the foregoing, it can be appreciated that there is a substantial need for a method and apparatus of dynamic allocation of resources for broadband services in a wireless communications system that efficiently provides high-quality broadband packet services to a large number of users and that solves the other problems described above.

DESCRIPTION DETAT.T. &A? T? T? THE INVENTION The disadvantages of the technique are largely solved by the method and apparatus of dynamic allocation of resources for broadband services in a wireless communication system. The communications system can have a number of cells, each of which has multiple sectors. Each sector can contain a number of communication sites. The information is transmitted in its programmed time frame to avoid interference between sectors and cells, and different degrees of concurrent packet transmission and can be programmed for different classes of communication sites. The communication sites can be classified based on the quality of reception, for example by comparing their ratio of signal to measured interference (SIR) with a SIR threshold. With these and other advantages and features of the invention that will become apparent in the following, the nature of the invention can be more clearly understood with reference to the following detailed description of the invention, the appended claims and the various drawings appended hereto. .

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a typical wireless communication system, suitable for one embodiment of the present invention.

Figure 2 shows a cell distribution and a frame structure according to an embodiment of the present invention. Figure 3 shows the order of allocation of slots or slots for the method of allocating alternate resources according to an embodiment of the present invention. Figure 4 is a block diagram of a terminal classification process according to an embodiment of the present invention. Figure 5 shows the order of use of sub-frames and minimarks in the method of the designation of alternating, enhanced resources, according to one embodiment of the present invention. Figure 6 is a block diagram of a time-slot programming process according to an embodiment of the present invention. Figure 7 shows a typical antenna pattern, with a back-to-back ratio of 25 dB and a beam width of 60 °, suitable for use with one embodiment of the present invention. Figure 8 shows the impact of the base station antenna bandwidth on operation and range according to one embodiment of the present invention.

Figure 9 shows the impact of the ratio versus back of the base station antenna on operation and range according to one embodiment of the present invention. Figure 10 shows the impact of the ratio versus back of the terminal antenna on operation and range according to an embodiment of the present invention.

DESCRIPTION PKTftT. ftPft The present invention is directed to a dynamic method and apparatus for allocating resources for broadband services in a wireless communication system. In particular, a resource allocation algorithm, hereinafter referred to as an enhanced alternate resource allocation method (ESRA) is used for broadband wireless networks with directional antennas at base stations and at terminals. The ESRA method uses alternate allocation of resources (ESRA) but also considers the quality of reception in terminal positions. This is done by categorizing terminals into multiple classes based on the ability to tolerate concurrent packet transmissions. The bandwidth is divided into multiple time slots, each of which has a number of minimarcos which allow different degrees of concurrent transmissions. Packages of different classes are sent in corresponding miniards. According to the ESRA method, concurrent transmissions are maximized to a tolerable degree by the resulting terminals for improved operation, and at the same time the main interference with channels in the networks is avoided when the same frequency band can be used in each sector of each cell. In an environment of reasonable radius, with practical antenna patterns and choices of system parameters, the ESRA method can provide 98.69% range, and provides maximum performance of 36.10% per sector, with a probability of successful packet transmission. one, given a specific SIR thold. This translates into a very large network capacity and a high quality of service that shows the applicability of the ESRA method to support real-time traffic, such as voice and video, as well as data. Although the system described in detail is a fixed broadband packet switched network using TDMA with user data rates of 10 Mb / s, the link lengths typically less than 10 kilometers and an operating frequency in the range of 1 At 5 GHz, the ESRA method, of course, can be used in other wireless communication systems. Now with detailed reference to the drawings in which the similar parts are designated by like reference numbers through them, Figure 2 shows a service area in a wireless network divided into hexagon-shaped cells. Each cell is further divided into multiple sectors numbered 1 to 6, and each sector is covered by a localized sector antenna with a base station (BS) not shown in Figure 2, in the center of the cell. Due to colocalization, sector antennas are also referred to as BS antennas. The terminals (users) can use directional antennas mounted on top of the roofs and pointing to the respective BS antennas. The bandwidth of each BS antenna may be just wide enough to serve the entire sector, while the terminal antenna may have a smaller bandwidth to suppress interference. The forward versus backward ratio (FTB) for BS and the terminal antennas is assumed to be finite. The time is divided so that one packet can be transmitted in each slot, and the downlink and the uplink between terminals and BS is provided by time division duplex (TDD) using the same radio spectrum. In the context of packet switched networks, time intervals naturally become bandwidth resources. The time intervals necessary to be dynamically assigned to various transmitters to send data packets such as a given SIR can be obtained at the receiver proposed for successful reception. This results in the concept of dynamic allocation of resources (DRA). The problem of allocating time intervals to obtain some optimal performance and at the same time satisfying a SIR requirement can be considered mathematically non-polynomial (NP) complete or hard, which implies a very high degree of computational complexity to derive optimal assignments . In the fixed wireless network of the present invention, the sectorization of cells and directional antennas in fixed terminal positions are used to reduce the interference between neighboring vectors and cells through the Alternate Resource Allocation Method (SRA). This results in a distributed DRA algorithm where the same (shared) radio spectrum is used for each sector in each cell on a dynamic time basis. With the use of directional antennas to suppress interference, the SRA method is particularly effective to avoid interference both between cells and within the cell. Nevertheless, based on terrain and fading, a certain terminal (for example, home) can constantly be unable to receive a signal with a satisfactory SIR due to its fixed position. The transmission for other terminals must always be successful. Therefore, the terminals in "good" and "bad" positions must be addressed in accordance with different time-zone reuse patterns, which is called time interval reuse division (TSRP) which allows many BS transmit simultaneously if the proposed receiver terminals are located in good positions. When the receiver positions are poor, some BSs will be programmed to transmit at the same time so that a threshold SIR target can be satisfied for a successful reception at the receiving ends. The TSRP divides the time frame (i.e., the bandwidth) into a dedicated portion and a shared portion. Most of a packet is transmitted between four neighboring cells during each time slot in the dedicated portion and up to three packets can be transmitted simultaneously in each cell in the shared portion. The purpose is to assign terminals in "good" and "bad" positions to use time slots in the dedicated and shared portion, respectively. Because of the bandwidth division in the dedicated and shared portion, many terminal positions with moderate reception quality may be overprotected when they transmit in the dedicated portion or may not receive the packets successfully when they are sent during the shared portion. This results in a potential waste of bandwidth. The present invention improves the SRA method when considering the reception quality of the terminals. This method of allocating enhanced alternating resources (ESRA) has the ability to avoid main interference as does the SRA method, and makes use of the knowledge of reception quality in terminals to improve performance and maintain the probability of success of one for transmission package. As discussed in detail in the following, ESRA also provides near complete coverage for a set of typical radio and system parameters. Referring again to Figure 2, with the regular hexagonal cell distribution, each cell is divided into six sectors, each of which is served by a BS antenna with a beam width of 60 °, and the terminal antennas may have Beam width smaller than 60 °. In the SRA method, the time slots are grouped into 6 sub-frames and the sectors are marked by one to six counter-clockwise, as shown in Figure 2. Sector marking patterns for adjacent cells are made rotate 120 °, which generates a group of three cells whose patterns can be repeated throughout the system. Note that the time frame shown in Figure 2 is applicable to both a downlink and an uplink, which are provided by TDD using the same spectrum. Each of the sectors allocates time slots to transmit packets to or from their terminals according to a special order shown in Figure 3. It is assumed that the BS is informed when a terminal needs to send packets, perhaps by means of a channel of multiple access separated or by double requests. For example, sector 1 first programs packets for transmission in time intervals of sub-frame 1 (indicated by a). If there is more traffic to send, then use subframe 4 (£ >;), sub-frame 5 (C), etc., up to sub-frame 6. { f) The reasoning behind this particular order is as follows. If interference due to concurrent transmission of packets in the same cell can be tolerated, then after using all the slots in the first subframe a, sector 1 must use the first sub-sector of the opposite sector (sector 4) in the same cell to make the best use of BS directional antennas. Following this, the time intervals in the first sub-frames are used for the sectors after the opposite sector. To avoid interference due to antenna overlap patterns from neighboring sectors, their first sub-frames are used as the last resort. For simplicity (although it causes very little degradation of operation), Figure 3 does not show the assignment of the left and right side of the sub-frames. The order of allocation for the next sector is "alternated" by a rotation to the right by a sub-frame based on the order for the previous sector. The order of assignment, regardless of the associated sector, is generally referred to as the "alternate" order. It is easy to see from figure 3 that if all the sectors have traffic load of less than one sixth of the total capacity of the channel, all the packets are transmitted in different time frames (labeled "a" in each sector), so that interference is not caused within the same cell. Of course, as the traffic load increases, the packets will be transmitted simultaneously, and this increases the level of interference. However, the alternate order takes advantage of the characteristics of the directional antennas to allow multiple transmissions of concurrent packets and at the same time reduces interference within the cell. In addition to handling interference within the cell, the SRA method helps avoid interference from main sources in neighboring cells. This is particularly true also when the traffic load is low to moderate. Consider the downlink for sector 1 in the middle cell of Figure 2. Sector 2 in the lower cell and sector 3 in the upper cell are the main interference surfaces. When examining the alternate order for sector 1, 2 and 3 it is noted that they will not transmit simultaneously, and this will not interfere with each other, provided that each one has a traffic load of less than one third of the total capacity of the channel (ie, using only a and b subsets for transmission). The same comment also applies to the uplink, where sector 2 and 5 of the lower cell in Figure 2 now become the main sources of interference. Due to the symmetry of the alternate order and the distribution of cells, the comment is applied to each sector in each cell. For a given radio environment and antenna characteristics, the SRA method can be used together with a control mechanism to improve the SIR and receive ends. Specifically, the control limits packet transmissions only in the first sub-frames in the alternate order for each sector. For example, if at most three packets can be sent simultaneously by several BS or terminal antennas in the same cell to ensure the reception quality required in the given environment, only the time slots in the sub-frames, a, b and c, as indicated in Figure 3 would be used for transmission in each sector. The control limits the degree of current transmissions and thus the amount of interference, to obtain an objective SIR for the desirable quality of service. The ESRA method may include the following components, described in detail below: terminal classification; cell and sector selection; minimarco structure and programming mechanism; and selection of minimarco sizes.

Terminal Classification The ESRA method uses the same sector marking as the SRA method shown in Figures 2 and 3. The basic idea of terminal classification in the ESRA method is to categorize terminals based on their ability to tolerate varying degrees of concurrent packet transmission. according to the alternate order. The tolerance depends on the reception quality of the terminal positions, which in turn depends on the distance between the BSs and the terminals, the transmission power, the characteristics of the antenna, the terrain and the fading. For the distribution in Figure 2 with six sectors per cell, there are six levels of concurrent transmission. Correspondingly, terminals are categorized into six classes, indexed from one to six. As shown in Figure 3, each time frame has 6 sub-frames, indexed from 1 to 6. Suppose that J ^ is the index of the lowest sub-frame for sector i in the alternate order. For example, J? 2 = 3, J32 = 6, 33 = 1, 3, = 5, J35 = 4 and 3 ^ = 2 for sector 3, because first use the intervals in sub-frame 3, 6, 1 and so on successively, as shown in figure 2. Also, for c = 1,2, ..., 6, suppose that Jc (j) c. { 1, 2, ..., 6.}. denotes a set of sectors allowed to transmit in sub-frame j when each sector can use only the first of sub-frames c in the alternate order for transmission (which results in concurrent c-packet transmissions in each cell). For example, J2 (l) =. { l, 4 } , J3 (l) =. { 1,4,3} , J4 (3) =. { 3,6,5,1} and I5 (3) =. { 3,6,5,1,2} . Assume that the system can activate one of a set of BS antennas to send a special signal, such as a path for a pilot tone, for measurement purposes. Figure 4 illustrates a classification procedure for a terminal located in sector i according to one embodiment of the invention. After starting in step 400, the process sets C = 6 and k = 1 in step 410. The process then establishes j = J1 ^ in step 720. The system instructs the BS antenna in sector i, where it belongs the terminal, to transmit a special signal. In step 422, the strength of the received signal is measured at the terminal position. Subsequently, the BS antennas for all sectors in Jc () are arranged to transmit simultaneously and the power received in the terminal is measured in step 425. The SIR in the terminal where all the sectors in Ic (j) transmit, it can be obtained from these two measurements in step 427. In step 430, if the SIR is less than a threshold required for satisfactory signal detection, the process continues with step 470. Otherwise, the process continues with step 440. In steps 440 and 480, the terminal is categorized as a class C terminal and the procedure is completed if 7c = C. In other words, the system can sustain interference with concurrent packet c transmissions in accordance with the alternate order. Otherwise, in step 450, it increases with 7c in 1 and the process advances to step 420 to verify the SIR when it is transmitted in the next sub-frame. If in step 470 C > 1, c * decreases by 1 and 7c is set to 1 in step 460 before step 420 is repeated. Otherwise, in step 485, the terminal can not be serviced by the SRA method because the terminal is unable to meet the SIR threshold - even when a packet is transmitted in each cell at a time. Therefore, the procedure is stopped at step 490. For a typical radio environment, it is not possible to attend to less than 1.5% of terminals located uniformly by the SRA method. In these cases, terminal antennas with an improved FTB ratio, or sophisticated digital signal processing techniques can be used to lower the SIR requirement, to ensure satisfactory reception.

In practice, terminal classification can be performed when the service is installed in the terminal position. In addition, the classification of each terminal must be periodically updated to monitor reception quality through measurements and statistics collection. Periodic monitoring would be useful because the radio environment tends to change over time due to, for example, seasonal fluctuations and the addition of objects placed by man in the radio path.

Cell and Sector Selection It is well known that cell selection can improve the quality of signal reception. To take advantage of the macrodiversity in the ESRA method, each terminal selects its cell and sector, which may not necessarily be the closest in distance, according to the fading and the programmed algorithm in use. Specifically, for each terminal, the ESRA method applies the terminal classification procedure presented above to determine a terminal class for various combinations of sectors and cells in the vicinity of the terminal. Then the terminal chooses a source sector and the cell that provides the terminal class with the largest index (ie, that can tolerate the highest degree of concurrent transmission). If multiple combinations of cells and sectors provide the same terminal class, the one with the highest SIR is chosen. With this classification and selection of cell terminals and sector, you can successfully receive packages for the class C terminal, in terms of satisfying the required SIR, if each sector uses the first sub-frames c in the alternate order (which provides concurrent c-packet transmissions in each cell). For this reason, the frame structure in Figure 2 can be modified so that packets for each terminal class can now be transmitted simultaneously to the maximum tolerable degree of concurrent transmissions in order to improve performance without degrading the probability of success of the package reception.

Frame structure and programming mechanism Each time frame in the ESRA method consists of six sub-frames, indexed from 1 to 6 in Figure 5. Each sub-frame is further divided into six "mini-frames", which are also marked from 1 to 6. Each mini-frame with the same label It consists of a multiple but fixed number of time intervals in each sub-frame. The sizes of the minibars are chosen to coincide with the expected traffic demand of the terminal classes and each sector uses the sub-frames according to the alternate order, given by "a" to "f" in figure 5. It is important to do Note that the time intervals of only those minimaarks marked with a continuous line are available for the corresponding sector indicated on the left side of the figure. Clearly, by varying from one sub-vessel to another, each sector is allowed to schedule the packet transmission on one or more minibars in some sub-frames, but not in others. For example, sector 2 can use all the sub-frames of sub-frame 2, but can program transmissions only in sub-frame 5 and 6 in sub-frame 3. The other mini-frames in sub-frame 3 are not available for sector 2. There are different degrees of Concurrent package transmission in different mini-stores. For c = 1, 2, ..., 6, as many packages c are transmitted simultaneously during the minimarco C in each sub-frame. At one extreme, only one packet is transmitted in each cell during mini-frame 1, while at the other end, up to six packets are sent during mini-frame 6. Different mini-frames allow different degrees of concurrent packet transmissions. Therefore, the minimarco structure is compatible with the terminal classification because the packets for terminals C transmitted in the mini-C will be successfully received as verified in the classification procedure. In fact, as discussed in detail later, the transmission of packets for the class 7c terminal in the minimarco c with c <; k, referred to as "improved compartment", will also be received successfully. In the ESRA method, the procedure shown in Figure 6 is requested for each time frame in each sector in each cell to assign varying time intervals in the framework for pending packets for transmission. Once a packet is programmed for transmission in a time interval, the interval becomes unavailable for the other packets. After starting in step 600, the procedure establishes c = 1 ei = c in step 610. In step 620, the sector programs class i terminal pending packets for transmission in the available time slots of mini-frame C, starting from the first sub-frame in the alternate order (indicated by aaf) and according to the availability of minimarts in the sub-frames for the sector, as shown in figure 5. Programming continues until: (i) all the intervals have been assigned of time available in minimarco c in step 630; or (ii) all pending packets for the terminal class for transmission are programmed in step 640. If condition (i) occurs, the process advances to step 660, otherwise, the process advances to step 650.

In step 660, if c < 6, then increment c in 1 and i adjust to c in step 670 before advancing to step 620. Otherwise, the procedure stops at 690 since all the time slots available in the time frame have been assigned. In step 650, if i < 6, then i is incremented by 1 and the process advances to step 620 to schedule the transmission of packets to the next terminal class in the minimarco C. Otherwise, the procedure stops at step 690 since all pending packets must be programmed for transmission. It is worse that as long as time intervals are available, the packets are transmitted by the enhanced compartment to further improve the SIR at the receiving ends.

Selection of Minimarco Sizes The minimarco structure can be considered as a division of the bandwidth into multiple "channels" which allows different degrees of concurrent packet transmissions tolerable in terms of SIR by different terminals. To maximize the operation of the system, mini-frame sizes must be chosen to match the traffic load from the respective terminal classes. Without loss of generality, consider that the terminals of all classes have an identical traffic load. Suppose that oi is the fraction of terminals class i (in relation to the total number of terminals served by the ESRA method) in the complete network for i = 1 to 6. Also, suppose that Nt is the "target" number of time intervals in each frame subframe, which is determined by considering the delay requirements of the package, programmed of general processes and so on. Also, suppose that the minimarco i in each subframe has r ^ time intervals. As explained in detail with respect to Figure 5, each sector can use the minimarco i in i different sub-frames. Therefore, to handle the uniform traffic load between terminals: where ß is proportionally constant and the rounding of the whole number is ignored at the present moment. Since: The following relationship is maintained: substituting this in the previous equation, for ni, you get that: where [x] indicates the integer closest to x. With these minimarco sizes, each subframe has: N -? n timeslots. The frame size is KN, where K is the number sectors in each cell, which is equal to 6 for what we have considered.

Operation Analysis of the ESRA Method Using the terminal classification method described here, the packet transmissions for each terminal class in its respective mini-frame will be successful. That is, the probability of success of the packet transmission is one in regards to the satisfaction of a specific SIR threshold. To analyze the packet operation for the ESRA method, assume that terminals of all classes have identical traffic loads and that there are always pending packets to be transmitted. Based on the size of each minimarse i, the maximum performance for class i terminals is in / KN packets per time interval in each sector. This is due to the fact that: (1) each sector can transmit during the minimarco i in í different subframes of each frame and (2) each packet transmission for the terminals class í in the minimarco i will be successful by definition of terminal classification. Therefore, the maximum performance in each sector for all classes of terminals is: ? n, N, a¡ / i - S KN KN. C jPHANTOM 4 Ignoring rounding for the whole number, and applying the fact that ai = 1 and -Nt ~ N, the maximum performance per sector is obtained by Since the probability of successful packet transmission for the ESRA method is one, its operation is limited only by the availability of pending packets associated with each class of terminal for a given mini-frame structure. As a desirable consequence, once the maximum operation is reached for sufficient traffic, the additional increase of the traffic load will not cause any degradation in the operation. Although it may seem that the division of bandwidth in minimarks in the ESRA method can lead to loss of "trunk efficiency", note that packets for class 7c terminals can be successfully transmitted during any minimark C available to the sector associated with q <7c. When such a packet is sent in the mini-frame, the SIR can actually be improved at the receiving ends. Such a division of minimarcos is called an "improved distribution". To demonstrate the improvement in SIR, suppose that F is the SIR threshold for a correct signal detection in a receiver. In addition, it uses Pj to denote the received signal or the interference strength from the BS antenna or sector j. Without loss of generality, consider a terminal in a particular sector i. As in the above, use J ,,, to denote the index of the lowest subframe in the alternate order for use by sector i in the time slot assignment. According to the terminal classification, the terminal is characterized as being of class 7c if 7c is the largest integer such that: for everything = 1,2, ..., 7c and j = 1.,. If a package for the class 7c terminal in sector i is transmitted in the mini-frame 1 < 7c, then the SIR in the receiver is given by where j '= ^ for some give me. { 1, 2, ..., l} because the sector can cause the miniards 1 in any of the first sub-frames 1 in the alternate order. Since 1 < k, which indicates different degrees of transmission of packages, I? (j) = I¡c (j) for any subframe j. This, certainly is valid for all j = Jim with 27? = 1, 2, ..., 1. When combining this and the fact that Ps = 0, the denominator in the equation for F must be less than or equal to that in the equation associated with F, therefore f > F. In other words, the improved distribution, or the transmission to the class 7c package in any minimarco C with c < 7c can satisfy the SIR detection threshold. Since it is possible that P3 = 0, or transmission at the lower power level, when a sector s does not have enough traffic to send, the improved deal actually improves the SIR at the receivers. In contrast, a similar analysis reveals that the transmission of class 7c packets during the time slots available in the minimarco c * z 7c, which is called "degraded cast" can not guarantee satisfactory SIR. That is, the degraded deal does not provide successful transmission of packets with a probability of one. For this reason, the programming algorithm described with respect to Figure 6 does not include such a distribution. However, the degraded deal can still be applied to packages without tight delay requirements. This is particularly true if the BS can program class 7c packets for transmission in time intervals in minimarco C > k when the traffic load is low enough and the degree of concurrent packet transmissions in the time intervals can be maintained so that it is not greater than 7c. It is important to note that packet transmissions through the degraded deal does not have an impact on the original transmissions, or those due to an improved distribution, because the degraded distribution does not increase the degree of concurrent transmissions. Therefore, the level of interference remains unchanged. In the worst case, if the packages are not successfully received the first time by the degraded distribution, they can be retransmitted in their corresponding or improved minimarcs.

.Results of Numerical Operation for the ESRA Method Typical radio and antenna parameters and a simulation model created with OPNET, a computer-aided engineering tool for networks and communication analysis developed by MIL 3, Inc., of Washington, DC, were obtained to obtain the fraction of terminals of different classes. Based on the fractions and on the assumption of uniform traffic between terminal classes, the results were then applied to calculate the maximum package performance for the ESRA method. A hexagonal cell distribution with two overlapping element antennas with a total of 19 cells was used. That is, an antenna of 12-cell outdoor superimposed elements is added to the configuration shown in Figure 2. Each cell is divided into 6 sectors, each of which is served by a BS antenna co-located in the center of the cell. Unless otherwise specified, the bandwidth (where the signal strength decreases by 3 dB) of each BS and the terminal antenna is 50 ° and 30 °, respectively, while each terminal antenna points directly to your BS antenna. Practical antenna patterns were used, such as one shown in Figure 7. Although the rear / side lobe is not shown, the signal reaching the rear / side lobe is attenuated according to the FTB ratio. Due to the superposition of antenna patterns, it is likely that certain terminals, especially those located at the sector boundary, will receive a significant amount of interference from neighboring sectors. Each radio path between a transmitter and a receiver is characterized by a path loss model with an exponent of 4 and a normal log fading. For the downlink, since there is only one radio path between all the BS antennas in the same cell (which are colocalized) and any terminal in the cell, the proposed signal and the interference must experience the same fade normal log and loss of trajectory. However, the fading from the BS antennas in other cells is assumed to be different and independent. Unless stated otherwise, the typical FTB ratios for BS and the terminal antennas (denoted by B and T) are 25 and 15 dB, respectively. The standard deviation for shadow fading is 8 dB. In addition, with standard modulation and equalization schemes, such as phase quadrature key shift (QPSK) and decision feedback equalization (DFE), the SIR threshold is selected for satisfactory detection which would be from 10 to 15 dB , up to a SIR threshold of 15 dB. For each packet transmission, if the SIR at the proposed receiver exceeded the threshold, the packet was considered successful. Only the statistics in the middle cell were collected and the following results were obtained for approximately 1,000 terminals placed uniformly across sector 1 of the central cell. After the classification method of figure 4, the following table 1 presents the fraction of terminals in various classes for the SIR thresholds of 15 dB.

Table 1. Fraction of Terminals in Different Classes Terminal class No BS selection With BS selection 1 0.1146 0.0813 2 0.5250 0.6375 3 0.0333 0.0479 4 0.0115 0.0208 5 0.0219 0.0292 6 0.1531 0.1698 Coverage 0.8594 0.9864 Operating 0.3402 0.3610 The results are included with or without BS and sector selection, referred to as "BS selection" briefly. The sum of the fractions for all classes provides the total fraction of terminals that can be served by the ESRA method, or "coverage", since the ESRA method can eliminate intracell interference completely by allowing only one transmission packet in each cell at a time, and the coverage is determined mainly by interference and intercell fading. On the other hand, the maximum performance depends strongly on the terminal fractions in various classes. That is, a high degree of tolerable concurrent transmissions results in greater performance. Without the BS selection, coverage is 85.94%, 14.06% of the remaining terminals can not be attended even when there is only one packet transmission in each cell at a time. In contrast, coverage increases to 98.64% with BS selection due to macrodiversity, and such coverage is adequate in practice. It is also interesting to note that table 1 shows that most of the terminals are in class 2 and that the smaller fractions are in classes 3 to 5. This is because the alternate order is particularly good to avoid interference within the cell as between cells when each sector transmits in the first two sub-frames in order. However, for higher degrees of concurrent transmissions, the amount of interference within the cell is increased due to antenna patterns superimposed between adjacent sectors in the same cell. 16.98% of class 6 terminals are likely to be located near BS with a favorable fading and are not affected by adjacent sectors. Figures 8 to 10 show the antenna bandwidth and the FTB proportions that can affect the operation of the ESRA method. Figure 8 shows the effect that the bandwidth of the BS antenna can have on the maximum operation and range. The range is insensitive to bandwidth, and maximum performance can be improved if the bandwidth of 60 ° is reduced to a smaller value. This is because a narrower bandwidth reduces the interference of neighboring cells and sectors. A bandwidth of approximately 50 ° for the BS antenna may be appropriate for a sector of 60 °. The bandwidth of the terminal antenna also varies from 10 to 40 °, while maintaining the BS antenna width at 50 ° and other system parameters does not change. The ESRA operation is also not sensitive to the range of the terminal antenna bandwidth because, insofar as the bandwidth is less than 60 °, each terminal antenna faces the front lobe of the BS antenna of a sector in the neighboring cells of the first antenna of overlapping elements, which contributes to most of the intercell interference for the terminal. As shown in Figure 9, which illustrates the operational impacts due to the FTB ratio of the BS antenna, the coverage is relatively insensitive to the FTB ratio of the BS antenna. On the other hand, as the FTB ratio increases, the interference decreases, which allows a high degree of concurrent transmissions and improvement of the maximum performance of the packet. However, when the FTB ratio reaches 25 dB, the additional increments of the proportion generate only a marginal performance improvement because other parameters, such as the terminal antenna FTB ratio and the SIR threshold, become dominant factors to determine the operation .

By contrast, Figure 10 shows that both the range and the operation depend strongly on the FTB ratio for terminal antennas. Generally, when the ratio is high, the inter-cell interference can be suppressed sufficiently so that almost all terminals satisfy the SIR threshold and the terminals can tolerate a high degree of concurrent transmissions. As a result, both the range and performance improve as the proportion of terminal FTB improves. In summary, the use of minimarcos by the ESRA system can apply various limits to control the degree of concurrent transmissions, depending on the quality of reception and the positions of the terminals. Using classification and ESRA terminal programs, packet transmissions for all classes of terminals can be successfully received given a specific SIR threshold. This is in contrast to the uncertainty of successful packet reception for the SRA method, the TSRP approach and most containment-based multiple access protocols. In addition, the operation of ESRA is stable due to its operation and successful transmission of packets which does not deteriorate with an excessive amount of traffic. For these reasons, the ESRA method can be used even for real-time traffic such as voice and video services. In addition, the probability of success for the transmission of a packet can help simplify call admission control and traffic handling to ensure a desired level of QoS. The operation of ESRA depends on the correct categorization of terminals. As the quality of a radio path between any BS pair and terminal can vary over time, perhaps due to seasonal fluctuation or man-made objects, the quality of reception can be periodically monitored and, when needed, a Terminal can be reclassified. To handle the temporal fluctuation, the ESRA method can use the enhanced allocation approach to retransmit packets (ie, to ensure that class C packets are retransmitted in the minimark 7c with k <; c) that they are not received properly the first time. For a reasonable radio environment, using practical antenna patterns and system parameters, the ESRA method provides 98.64% range and generates maximum performance of 36.10% per sector, with a probability of success of one for packet transmission. Although they have been illustrated, and specifically described in the present various. embodiments, it will be appreciated that the modifications and variations of the present invention are covered by the foregoing teachings and within the scope of the appended claims without departing from the spirit and scope proposed of the invention. For example, although the TDMA system is used to illustrate the various embodiments of the invention, it can be appreciated that other systems are within the scope of the invention. Similarly, although various embodiments of the invention refer to fixed terminal stations, it can be appreciated that the mobile terminal stations may be within the scope of the invention. Another example includes the number of sectors and cells discussed in the various modalities. It can be appreciated that different amounts of sectors or cells are also within the scope of the invention. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following:

Claims (38)

1. A method for operating a communications system having a plurality of communication sites and a service area divided into a plurality of sectors, the communications system uses a plurality of scheduled timeslots to avoid interference between the plurality of sectors, each Subframe is further divided into a plurality of minimarks, the method is characterized in that it comprises the steps of: scheduling a first degree of concurrent packet transmissions in a first mini-frame for a first class of communications sites located within each sector; program a second degree of concurrent packet transmissions in a second mini-frame for a second class of communications sites located within each sector, the degree of sector is different from the first degree; and communicate the packages according to the program.

The method according to claim 1, characterized in that it comprises the step of: classifying the plurality of communication sites into a plurality of classes including the first class and the second class.

The method according to claim 2, characterized in that the classification step classifies a communications site based on the reception quality of the communication site.

4. The method according to claim 3, characterized in that the classifying step classifies a communications site based on the signal proportion with respect to the interference of the communication site and at least a threshold of the signal proportion with respect to interference .

5. The method according to claim 4, characterized in that the classification step allocates a communications site to the classification that has the highest possible packet transmission and still maintains the probability of success and threshold for the proportion of signal threshold with respect to interference.

6. The method according to claim 5, characterized in that the threshold success probability is one.

The method according to claim 2, characterized in that the classification step is performed at the beginning of the communication system operation.

8. The method according to claim 2, characterized in that the classification step is performed periodically during the operation of the communication system.

9. The method according to claim 2, characterized in that the mini-frames in a sub-frame have different sizes.

The method according to claim 9, characterized in that the minibars are assigned a size that is selected based on the expected traffic from the associated class of communication sites.

The method according to claim 9, characterized in that the minibars are assigned a size that is selected based on the number of communication sites in the associated classes.

The method according to claim 1, characterized in that the packet transmissions for a class of communications sites can be transmitted in an alternative mini-frame associated with another class of communication sites having a lower degree of concurrent transmission.

The method according to claim 12, characterized in that the packet transmissions for a class of communication sites are transmitted in the alternative mini-frame while the alternative mini-frame is not being used up to its capacity.

14. The method according to claim 2, characterized in that it further comprises the step of: selecting an appropriate sector for a communications site based on the classification of the communications site in a plurality of different sectors.

15. The method according to claim 1, characterized in that the programming steps create an excess information transmission program that indicates when excess information will be transmitted for an initial sub-frame in other sub-frames and minimarcs.

16. The method according to claim 15, characterized in that the other sub-frames are selected according to a special order.

17. The method according to claim 16, characterized in that the special order is general when ordering all sub-frames from a minimum level of interference to a maximum level of interference.

18. The method according to claim 17, characterized in that the special order is generated using an alternate resource allocation protocol.

The method according to claim 18, characterized in that the service area has a plurality of cells, and each cell has six sectors.

The method according to claim 19, characterized in that the system has six sub-frames, with each sector within a cell assigned to a different sub-frame.

21. The method according to claim 20, characterized in that the pattern is generated by rotating each cell 120 °.

The method according to claim 21, characterized in that the initial sub-frame for sector 1 is sub-frame 1, and the special order comprises sub-frames, four, five, three, two and six.

23. The method according to claim 22, characterized in that when the initial sub-frame is one of the two to six sub-frames, the alternating resource allocation protocol alternates the special order in a sub-frame, respectively.

24. The method according to claim 23, characterized in that the communication sites are divided into six classes, each of the six classes corresponds to one of the six sub-frames.

25. The method according to claim 1, characterized in that the communication sites are fixed.

26. A method for reusing a common frequency in each sector of a communications system having a plurality of communication sites, characterized in that it comprises the steps of: identifying the main sources of communications interference for the communication sites located within each sector; evaluate the quality of the communications of each one of the communications sites located within each sector; and programming packet transmissions that include concurrent packet transmission, in all sectors to avoid communication interference and to obtain a quality communications threshold.

27. The method according to claim 26, characterized in that the step of scheduling program packet transmissions to maximize the transmissions of concurrent packets within a cell.

28. A communications system and having a plurality of communication sites and a service area divided into a plurality of sectors, the communications system uses a plurality of scheduled timeslots to avoid interference between the plurality of sectors, the system is characterized in that it comprises: a first class of communication units operatively associated with a service area for communication between the communication sites using at least one time frame; a second class of communications units operably associated with the service area for communication between the communication sites using at least one time frame; a programmer to program a first grade of concurrent packet communications for the first class of communication sites and schedule a second grade of concurrent packet communications for the second class of communication sites, the second grade is different from the first grade.

29. The system according to claim 28, characterized in that the programmer generates a transmission program of excess information.

30. The system according to claim 29, characterized in that the excess information transmission program indicates when excess information is to be transmitted for an initial sub-frame in the other sub-frames. >

31. The system according to claim 30, characterized in that the other sub-frames are selected according to a special order.

32. The system according to claim 31, characterized in that the spatial order is generated by ordering all sub-levels of interference minimum sub-levels up to a maximum level of interference.

33. The system according to claim 32, characterized in that the special order is generated using an alternate resource allocation protocol.

34. The system according to claim 33, characterized in that the service area has a plurality of cells and each cell has six sectors.

35. The system according to claim 34, characterized in that the system has six sub-frames, with each sector within a cell using a different sub-frame.

36. The system according to claim 35, characterized in that a pattern is generated by rotating each cell 120 °.

37. The system according to claim 36, characterized in that the initial sub-frame for sector one is sub-frame one, and the special order comprises sub-frames four, five, three, two and six.

38. The system according to claim 37, characterized in that the initial sub-frame is sub-frames two to six and the alternate resource allocation protocol alternates the special order in a sub-frame.