MXPA01001852A - Method and apparatus for multiple access in a communication system - Google Patents

Abstract

A communication system is comprised of three communication resources:a contention-type access block (112), a non-contention access block (114) and a second non-contention access block called a reserved block (110). Each time that a remote unit (104) has a block of data to transfer to a hub station (100), the remote unit (104) sends the block of data over the contention-type access block (112). The remote unit (104) also sends a corresponding notification message over the reserved block (110). If the hub station (100) receives the notification message but not the block of data, the hub station (100) sends a response message to the remote unit (104) which designates the resource within the non-contention access block (114). The remote unit (104) sends the block of data o ver the designated resource.

Description

METHOD AND APPARATUS FOR MULTIPLE ACCESS IN A COMMUNICATION SYSTEM BACKGROUND OF THE INVENTION I. Field of the invention. This invention relates in general to communication systems. More specifically, the invention relates to multiple access communication systems. II. Description of the related technical field. The use of wireless communication systems for the transmission of digital information is increasingly diffused. In a wireless system, the most precious resource in terms of cost and availability is usually the wireless link itself. Therefore, one of the main design objects in designing a communication system comprising a wireless link is to efficiently use the available capacity of the wireless link. In addition, it is also convenient to reduce the delay related to the use of the link. In a system in which multiple units compete for finite system resources, a means must be developed to regulate access to those resources. In a digital information system, remote units tend to generate over-amplified information. The ovemplified information is characterized by having a traffic index that goes from high to average, which means that blocks of information are transferred during short periods interposed between significantly longer periods of inactivity. The dedication of an individual communication channel to each active unit does not result in efficient use of the capacity of a system in which the units generate over-amplified information because, during those periods when the remote unit does not use the system, the assigned resources remain inactive. The use of dedicated channels can also impose an immutable limit on the number of remote units that the system can use simultaneously, notwithstanding the usage patterns of the remote units. In addition, the use of dedicated channels can cause unacceptable delay if the portion of resources allocated to each remote unit is so small that data transfer rates are significantly compromised. The characteristics of incoming and outgoing traffic tend to differ significantly in a digital information system. For example, in a system providing wireless Internet services, the typical outgoing transmission from a remote unit is relatively short, such as the request of a Web page.

However, the typical incoming transfer of information to a remote unit tends to be quite large. For example, in response to the Web page request, the system may transfer a significant amount of information. Because the characteristics of inbound and outbound links are very different, you can increase system efficiency by developing two different protocols for inbound and outbound links. The ALOHA random access protocol was developed for use on the outbound link from a remote unit in a digital information system. The basic idea of ALOHA is quite simple: remote units transmit whenever they have information to send. If the remote units are using a communication resource that only a remote unit can access at a time, the information from each remote unit is destroyed if two units transmit at the same time, causing a collision. In a system where the remote unit can verify the random access transmissions, it is possible for the remote unit to verify the transmissions in order to determine whether its transmission has been the victim of a collision. In a system in which the remote unit does not verify, or can not verify the random access transmissions, it is possible for the remote unit to detect a collision based on the expiration of a timer without acknowledgment of a message received from a central station in response to the transmission. In accordance with the standard operation of ALOHA, whenever a collision occurs, the remote unit waits a random amount of time and retransmits the information. The duration of the wait is random, so that the remote units that suffer the collision do not generate collisions in loc step again and again. Figure 1 is a time relationship diagram showing the operation of a pure ALOHA system with multiple random access. In Figure 1, five remote units designated as A, B, C, D and E are information transmission packets within a common communication channel. As long as two remote units transmit at the same time, a collision occurs between the two and both transmissions are lost. In a pure ALOHA system, if the first bit of a new transmission is superimposed just on the last bit of a transmission that is already in progress, both transmissions are completely destroyed and both have to be retransmitted later. For example, in the frequency modulated (FM) channel shown in Figure 1, where two packets can not be transmitted simultaneously, a packet 12 transmitted by the remote unit B collides with a packet 10 transmitted by the remote unit A and with the packet 14 transmitted by the remote unit C. The remote unit A must retransmit the information in the packet 10, the remote unit B must retransmit the information in the packet 12 and the remote unit C must retransmit the information in the packet 14 Figure 1 shows the remote unit C retransmitting the packet 14 as the packet 14R. In a pure ALOHA system, if the average transfer rate is low, most of the packets are transferred without collision. While the packet transfer rate begins to increase, the number of collisions increases and, therefore, the number of retransmissions also increases. While the load of the system increases linearly, the probability of retransmissions and multiple retransmissions increases exponentially. At some point, as the system load increases, the probability of a successful retransmission drops below a reasonable number and the system becomes practically inoperable. In a pure ALOHA system, the best use of the channel that can be achieved is approximately 18%, the so-called maximum channel utilization. Below 18%, the system is not maximized. Above 18%, the number of collisions increases in such a way that the performance of the system begins to fall. The operation above the maximum utilization of the channel is called overutilization of the channel. In conditions of overuse of the channel, the average delay of the system increases rapidly while the performance of the system falls and the stability of the system is compromised. The introduction of a geosynchronous satellite link within a digital communication system complicates the multiple access dilemma. The use of a geosynchronous satellite normally introduces a delay of 270 milliseconds (msec) between the transmission of a signal from a remote unit and the reception of that same signal at the central station. For this reason, scheduled access schemes that require the remote unit to request system resources before initiating each transmission introduce approximately half a second of delay in each transmission. For the frustrated user of the system, the delay associated with the scheduled transmissions is quickly evident. If the ALOHA system is instrumented in a satellite system in which the remote units can not verify, or do not verify the random access channel, in case of collision, the remote unit does not know about the collision for at least 540 ms. In addition to the delay in the notification, the remote unit should normally wait some random amount of time before retransmitting the data to avoid the closed rows in the retransmissions.

The retransmitted signal is subject again to the time delay of 270 msec. The cumulative delay of such transmission can easily exceed one second. In a fully loaded system, the delay may be significantly longer due to the increased likelihood of repeated collisions. Although these delays are not incurred in each transmission, when they happen they can be discouraging for the user. Therefore, there is a need for a multiple access system that provides for the profitable use of system resources, as well as a tolerable delay.

Compendium A communication system comprising three communication resources: a containment-type access block, an access block without containment and a second access without containment called a reservation block. Each time a remote unit has a block of information to be transferred to a central station, it sends the information block in the containment-type access block. It also sends a corresponding notification message in the reservation block. If the central station receives the notification message but not the information block, it sends a response message to the remote unit, which designates the resource within the access block without containment. The remote unit sends the information block in the designated resource.

BRIEF DESCRIPTION OF THE DRAWINGS The features, objects and advantages of the invention will become more apparent from the following detailed description, when taken into consideration together with the drawings, in which the parts are identified with the same numerical references that are used consistently and where: Figure 1 is a time relationship diagram showing the operation of a pure ALOHA system with multiple random access; Figure 2 is a block diagram illustrating the system according to the invention; Figure 3 is a conceptual diagram showing the allocation of communication resources according to the invention; Figure 4 is a diagram of the operating process showing the operation of the remote unit; and Figure 5 is a diagram of the operating process showing the operation of the central station.

Detailed description of the invention One of the problems faced by random access schemes is that, in the event of a collision, the remote unit may not know about the collision for some time. The central station can not detect which remote unit is involved when a collision occurs and, therefore, can not immediately notify the affected remote units when a collision occurs. Therefore, unless the remote unit can verify the random access transmissions in some way, the remote unit waits for the confirmation message from the central station. If the time corresponding to the time expires and the confirmation message is not received, the remote unit assumes that a collision took place. In a pure ALOHA system, the remote unit also waits for a random period of time before attempting retransmission after a collision is considered to have occurred. The delay introduced by retransmission and possible multiple retransmissions can become quite intolerable. The invention provides a multiple access means and a method that reduces or eliminates the excessive delay introduced by multiple retransmissions. A resource reservation block is used only to notify the central station whenever a remote unit first tries to access the system in a containment-type access communication resource. The notification of the central station allows the station to detect accurately when a collision occurs due to another type of failure and to identify the remote units involved in the collision. When a collision occurs, the central station assigns each remote unit involved in the collision a resource within a non-containing communication access in which the remote unit retransmits the information block. The resource is preferably dedicated to the remote unit and, therefore, the retransmission of the information block is not subject to the risk of collision. In this way, because the notification message and the retransmitted information block are transmitted through communication resources without containment, virtually no block of information is subject to more than one collision. In addition to decreasing the delay time associated with the retransmission process, contention-type resources are also downloaded to the extent that they do not require a large volume of retransmissions. Therefore, the probability of collisions in the containment-type access block is reduced. Figure 2 is a block diagram illustrating a system according to the invention. In Figure 2, the central station 100 provides communication resources to a plurality of remote units 104A-104N. Remote units 104A-104N can be nodes in a local area network, home computers, laptops, two-way paging devices, wireless fax machines or printers, digital readout equipment, or any form of unit that processes digital information. The link between the central station 100 and the remote units 104 comprises the satellite 102. The outgoing signals from the remote units 104 are transmitted to the satellite 102 where they are retransmitted to the remote units 104A-104N. The central station 100 can, for example, connect directly to an Internet node to provide wireless Internet access, a public telephone switch or a private digital network. The remote units 104 may comprise or implement one or more processes that enable them to perform the functions of the invention. Also, the central station 100 may comprise or implement one or more processes that enable it to perform the functions of the invention. Processes may be incorporated, for example, into one or more integrated circuits, such as a specific application integrated circuit (ASIC), and / or may be incorporated into software or firmware routines that are executed by means of a microcontroller or another processor. The communication resources within the central station 100 can be quantified in a series of communication resources according to some of the plurality of well-known techniques. For example, communication resources can be divided into a series of CDMA channels. The CDMA channels can be defined as a series of pseudo random sequences, practically orthogonal. Each sequence in the series defines a separate communication resource that can be used by a remote unit to communicate with the central station. Alternatively, the system can use time segment channels to subdivide the communication resources. In a TDMA system, remote units are assigned a segment of time to transmit. By limiting transmissions to those that fall within the allocated time segment, remote units are able to share the communication resources provided by the central station. In addition, frequency modulation (FM), amplitude modulation (AM), or a combination of the above or many other communication techniques can be used to quantify communication resources.

Figure 3 is a conceptual diagram showing the allocation of communication resources according to the invention. The communication resources are divided into three blocks of resource allocation. A reservation block 110 comprises a set of resources assigned and dedicated individually to an active remote unit. The reservation block can be instrumented in any of several well-known non-containment access mechanisms in which transmission from a remote unit does not prevent another remote unit from communicating. For example, the reservation block may comprise a set of the spread spectrum multiplexed time channels or a set of FDMA or TDMA channels. The multiple access and communication format of the reservation block 110 may be different from the remaining resource allocation blocks. As described below, reservation block 110 is used to transfer notification messages from the remote units to the central station. The resources allocated to reserve block 110 are small compared to the total available communication resources. For example, in a preferred embodiment, the reservation block 110 consumes less than about 1% of the available communication resources. In other embodiments, the reservation block 110 may consume less than 5%, 4%, 3% or even 2% of the communication resources available. The second resource allocation block is a containment-type access block 112. In a contention-type access, multiple users share a common channel or channels in such a way that conflicts may arise between them. In one embodiment, the contention type access block 112 comprises a set of random access resources. For example, the contention-type access block 112 may be an ALOHA access channel in which the user's transmissions are subject to collision. The contention-type access block 112 is used for the first attempts to transfer blocks of information from the remote units 104 to the central station 102. The third resource allocation block is an unrestricted access block 114. In an access of type without containment, transmissions from a remote unit do not prevent another remote unit from communicating. In one embodiment, the non-containment access block 114 is a programmed access block. The non-containment access block 114 is used to transfer blocks of information that were not successfully transferred using the contention-type access block 112.

When a remote unit sends a message containing an information block in the contention type block 112, it normally includes within the message the information block, the self-identification and other information used by the system. The information block itself may comprise, for example, Internet communications such as an email message or the request to a Web page, an electronic file, a short message, FAX information or other digital information. Each time a remote unit transmits a block of information using a communication resource within the contention-type access block 112, it also sends a notification message within the reservation block 110. The notification message is not subject to collisions. Because the notification message is generally significantly smaller than the corresponding information block, a relatively smaller amount of communication resources is needed to transfer the notification message. In one embodiment, the notification message takes one of two values. A first message may simply indicate the presence of the remote unit within the coverage area, and a second message may indicate that the remote unit is transmitting a corresponding information block. In the preferred embodiment, the communication format used in the reservation block 110 results in the central station having a high probability of successful reception. For example, the notification message must reach the central station with a relatively high signal to interference ratio. Each time a remote unit transmits a block of information in the contention-type access block 112 and a notification message in the reservation block 110, one of four results takes place. Either the central station receives both the information block and the notification message, or receives the information block but not the notification message or receives neither the information block nor the notification message, or receives the information block but not the notification message. In a preferred embodiment, the failure rate of the transmissions in the reservation block is less than 1 in 10,000. Also, in that preferred embodiment, it is convenient to limit the use of containment type access block 112 so that the collision probability is approximately 10%. Therefore, for at least 90% of the time, the central station successfully receives the information block and the notification message and transmits a confirmation message to the remote unit that transmitted the information block.

There is an extremely small chance that the central station will successfully receive the information block but not the notification message. In that case, the central station simply transmits an acknowledgment message to the remote unit that transmitted the information block in the same way, or the like, as if the notification message had been received. In the rare case where the central station does not receive either the information block or the notification message, the remote unit detects the timeout confirmation and can retransmit the information block in the containment-type access block 112. If it is maintained the load of the contention-type access block 112 so that the average collision rate is expected to be approximately less than 10%, the central station receives the notification message but not the information block for no more than about 10% of the weather. In this case, the central station transmits a response message to the remote unit that designates a resource within the access block without containment 114 in which the remote unit can retransmit the information block. The response message may be a specific message of the remote unit, a broadcast message or other type of message. The remote unit can be explicitly designated, implicitly, with a temporary identifier or using other means. In one embodiment, the non-containment access block 114 comprises a set of scheduled resources that can be temporarily dedicated to a selected remote unit. Upon receiving the response message from the central station, the remote unit retransmits the information block in the indicated resource within the access block without containment 114. The message comprises the information block and may also comprise other system information. The message comprising the information block sent in the access block without containment 114 may be different from that sent in the containment-type access block 112. For example, when using the resource within the access block without containment 114 assigned to the remote unit, the remote unit essentially identifies itself and it is possible that the inclusion of self-identification within the message itself is not necessary. The use of the non-containing access block 114 greatly reduces the likelihood that the information block is subject to more than one collision. During this process, the delays associated with waiting for the expiration of a confirmation timer, the waiting for random time periods, as well as the time spent on multiple retransmissions are avoided. The average delay associated with the transmission of a block of information is therefore diminished. In one embodiment, the resources dedicated to the access block without containment 114 comprise approximately a quarter of the communication resources available. By examining Figure 3, it can be seen that the resources allocated to the contention-type access block 112 are limited by the resources allocated to the reservation block 110 and the non-containment access block 114. Because the reservation block 110 represents only a small total percentage of the available communications resources, the use of the reserve block 110 does not significantly reduce the resources available to the containment-type access block 112. The use of the non-containment access block 114 downloads to the containment-type access block 112 by eliminating the use of containment-type access block 112 for the retransmission of information blocks. In doing so, the use of the non-containing access block 114 decreases the probability of collision in the contention-type access block 112, thereby increasing the total real transport speed of the system and decreasing communication resources spent on collisions .

In addition, the use of the access block without containment 114 significantly reduces the average delay time associated with the accession to the system, especially under relatively high load conditions. The use of the non-containing access block 114 also limits the retransmission process so that the worst probable hypothetical case of delay is limited to the time necessary to perform only one transmission. Note that this time delay, which is roughly equivalent to the delay of the second round trip associated with the transmission through a satellite, is the same delay associated with the perfectly programmed access method. Therefore, the access method illustrated in Figure 3 shows a much lower average delay than a perfectly programmed access technique. In addition, because the number of retransmissions is limited, the invention shows a lower average delay than the previous random access systems. Although the load in containment-type access block 112 must be limited in order to avoid channel over-use and reduction in performance, if the non-containment access block 114 comprises programmed channels, it can be used in its entirety without any of those concerns. In addition, the invention limits the likelihood of channel over-utilization and the possibility of unstable behavior of the system because the remote units do not attempt to continue access to the contention-type access block 112 after a collision occurs. Figure 4 is a diagram of the operating process showing the operation of the remote unit. The process begins in the start block 120. In block 122, the remote unit transmits a block of information in the contention-type access block. In a system using the pure random access ALOHA system scheme, block 122 may simply involve the transmission of the information block as soon as the packet is available. In other systems, block 122 may comprise the random selection of a random access channel from a set of available random access channels. In other systems, the block 122 may comprise the step of trying to capture the use of the contention-type access block by other units. In block 124, the remote unit transmits a notification message within the reservation block. The steps of the blocks 122 and 124 can be performed in the opposite order, or they can be performed concurrently. In block 126, the remote unit determines whether it has received the confirmation message from the central station within the time out confirmation period. In that case, the process ends in block 132. If not, in block 128 the remote unit determines whether it has received a response message from the central station designating a resource within the access block without containment. If so, the remote unit retransmits the information block in the resource designated in block 130. In the rare case that the remote unit does not receive a confirmation message or a response message, the process may continue back to the block. 122. Figure 5 is a diagram of the operating process showing the operation of the central station. The process begins in the start block 139. In block 140, the central station receives a notification message within the reservation block corresponding to a particular remote unit. Block 142 determines whether a corresponding information block within the contention type access block has been received within the specific period of time outside surrounding the receipt of the notification message. If so, the central station sends a confirmation message to the remote unit in block 148 and the process ends in end block 150. If not, the central station sends a message of compliance, ordering the remote unit to transmit in the access block without containment in block 144. In block 148, the central station receives the information block from the remote unit in the access block without containment. In block 148, the central station sends a confirmation message to the remote unit and the process ends in the completion block 150. In order to avoid channel overuse, the load in the containment type access block is generally kept below the threshold of maximum load according to the design of the system. If the system can predict the transmission probability of a remote unit with accuracy of at least approximately the equivalent of the maximum allowable load, system efficiencies can be increased by predictable scheduling. For example, if the system is designed to limit the load on the containment-type access block to approximately 10% of its total available capacity, and the central station can predict the transmission of a remote unit with an accuracy greater than 10%, the The central station can increase the total efficiency of system use by selecting a resource from the non-containing access block to be used by the remote unit, if the remote unit has a transmission to send. Using predictable scheduling, unrestricted access block resources are used less than their full capacity but increase system efficiency and stability. Frequently, the reception of a block of information from the remote unit is quickly followed by the reception of another block of information, especially in response to the intermediary message of the central station. Therefore, when a central station receives a block of information from a remote unit or a notification message associated with a failed transmission, the central station may include a predictable allocation of resources within the confirmation message. The predictable allocation of resources can designate a resource within the access block without containment. In this way, the confirmation message containing the predictable resource assignment tells the remote unit: "I received your last transmission and in case you have a transmission to send within the following X seconds, please send it within the access block without containment in resource Y ". In case the remote unit has a block of additional information to send, rather than using the containment type access block, the remote unit initially transmits the information in the indicated resource within the access block without containment. Also, when the central station transmits a block of information to the remote unit, the central station may include a predictable allocation of resources within the message containing the information block. In addition, the predictable allocation of resources can be sent as a separate message or a conformance message regarding a failed transmission. By using predictable programming, the containment-type access block 112 can also be downloaded, thereby decreasing the number of collisions as well as the average delay incurred within the system, and also increasing the performance and stability of the system. Referring again to Figure 5, in order to implement predictable programming, in block 148, the central station may include, within a confirmation message to the remote unit, a predictable resource allocation to be used by the unit remote for any transmission that it could generate during a limited period. If the original transmission failed, the central station may include within the message sent to block 144 an allocation of predictable resources that may be used for subsequent transmissions by the remote unit as long as they begin within a limited period. The inclusion or exclusion of the allocation of predictable resources in one of these messages or in another message can be a function of, for example, the current system load, the particularities of incoming or outgoing information of the user or the particularities of the unit remote In a modality, the remote unit indicates the convenience of a resource without containment within the message transferred in the containment resource. In another embodiment, the rigid separation of the containment-type access block 112 from the non-containment access block 114 in FIG. 3 is replaced by a movable spacing. If the contention-type access block 112 and the non-containment access block 114 use a common communication format, the central station can simply notify the remote units of the current channel that it divides the containment-type access block 112 from the access block no containment 114 in order to inform the remote unit of the current location of the movable partition. Under low load conditions, the communication resources allocated to the contention-type access block 112 may increase while the communication resources allocated to the non-containment access block 114 may decrease. In this way, the probability of collision decreases and the average delay introduced by the system also decreases. While the load of the system increases, the incidence of collision also increases and the amount of information transmitted in the access block without containment 114 increases. At this time, in order to accommodate the load increase in the non-containment access block 114, the communication resources allocated in the non-containment access block 114 can be increased. In an extreme case, if the load of the contention-type access block 112 becomes so high that it is dominated by the collision, the communication resources allocated to the contention-type access block 112 can be minimized or even eliminated. In that case, each transmission in the contention-type access block 112 generates a collision, and the system is reduced to a scheduled system based on the use of the reservation block 110 as a means to request a scheduled resource. The use of a movable delimitation between the resources allocated to the contention type access block 112 and the non-containment access block 114 allow the system to operate efficiently over a wide range of loading conditions. The backup block transmissions can be used to derive the time alienation (synchronization) and activate the information control for the remote units according to well-known techniques, whether or not the transmission of the reservation block indicates the transmission of an information block in the containment type resource. For example, when analyzing the transmission received in the reservation block, the central station can generate a command or information regarding the time adjustment, or activate the adjustment or information command for transmission to the remote unit using well-known techniques. Various time alignment techniques are disclosed in co-pending US patent application serial number 80 / 095,341, filed August 8, 1998, entitled: "Methods and apparatus for synchronization of time in a communication system". The use of the reservation block for these functions can be convenient because the remote unit can transmit real or fictitious messages in the reservation block without spending any additional resources of the system and without collision risk. By using the reserve block to instrument these overload functions, the load in the contention-type access block and the non-containment access block can be further decreased. In one modality, the reservation block reflects the amount of information transmitted in the containment-type resource. For example, in one embodiment, the transmission of the reservation block is a payload message indicating the number of packets transmitted in the containment-type resource. If the central station detects less than the indicated amount of information in the contention-type resource, the central station assigns a resource without containment of sufficient size to support the transmission of the amount of information that was not received and notifies the remote unit. The remote unit responds by retransmitting the information in the resource without containment. In this modality, if a remote unit transmits asynchronous information or other information where the remote unit can predict the need for communication resources, the remote unit can transmit a payload message in the reservation block indicating the transmission of the predicted amount of resources before the information is available for transmission. However, the remote unit does not transmit a corresponding message in the contention-type resource. Therefore, the central station receives the transmission of the reservation block but not the corresponding transmission of the containment-type resource and responds with a resource allocation without containment. The remote unit transmits the information in the resource without containment when the information is available without incurring in programming delay or the probability of collision in the containment-type resource. In addition, because the remote unit does not transmit a message in the contention-type resource, the load and the number of collisions in the contention-type resource are decreased.

In some cases, a remote unit transmits predictable information as well as a less predictable information flow. For example, a remote unit may concurrently transmit both a predictable speech signal rate and an unpredictable information signal. In that case, the remote unit may add the amount of predicted resources to the payload indication sent in the transmission of the reservation block. For example, if the remote unit has five information packets to transmit and can predict that it will have two additional voice packets to transmit, the remote unit transmits the five information packets in the contention-type resource and transmits a corresponding message in the block of information. reservation indicating that the seven information packets are being transmitted. The central station receives the transmission of the reserve block as well as the five data packets and programs the sufficient resource without containment to transmit the remaining two packets. In some systems, the total amount of reverse link power that can be transmitted concurrently is limited. For example, the reverse link power may be limited to a compression point of a satellite repeater or by government decision. If a large number of remote units attempt to access the system through the contention-type resource at any given time, the total power may exceed the reverse link power limit. In that case, it is convenient to limit the total amount of power that can be transmitted at a given time. One way to achieve this is by limiting the number of remote units that can transmit in any given containment-type resource segment. Therefore, rather than allowing remote units to transmit in each of the resource segments from within that containment-type resource, they are generally enabled to transmit only a subset of the possible contention-type resource segments. For example, if the contention-type resource is a jagged ALOHA system, the remote unit may be enabled to initiate retransmission in a subset of the possible transmission limits. If the resources are properly allocated, even if each remote unit that is enabled to transmit within a segment transmits within the segment, the total power is still within the allowable limit. In one mode, the remote units receive the enablement assignments according to the service designation class. In other modalities, the particular messages or type of messages are considered to have higher priority than others and the enabled assignments are distributed based on the type of message. The transmission in the reservation block does not have to be concurrent with the transmission of the containment-type access block. A transmission in the reservation block may indicate that the transmission was recently made in the contention-type access block, that a transmission is being performed concurrently in the contention-type access block or that the transmission will soon be made in the access block containment type. In another modality, the resources of the reserve block can be assigned unevenly among the remote units. For example, resources can be allocated based on a set of active and idle remote units. Active remote units are those remote units that are more likely to transmit information. Remote units at rest are those remote units that are less likely to transmit information. If transmissions are not received from an active remote unit for a long period of time, the central station can reclassify the remote unit as a remote unit at rest. If a transmission is received from a remote remote unit, the central station can reclassify the remote unit as an active remote unit.

Active remote units are assigned more frequent access to the reserve block than remote remote units. Likewise, the resources of the reserve block can be assigned among the remote units according to the quality of the service assigned to the user, the capacity of transmission of information of the remote unit, the previous use pattern of the remote unit or the period of time since the last transmission was received from the remote unit. The uneven allocation of reserve pool resources can help decrease the total wait time entered into the system by the use of the reservation block. Also, the total amount of the system resource dedicated to the reservation block may vary during the operation of the system. For example, the rigid separation of the reserve block 110 and the containment-type access block 112 and the non-containment access block 114 in Figure 3 can be replaced with a movable separation. By increasing the amount of resources allocated to the reservation block, the total waiting time of the system can be reduced due to the use of the reservation block. However, increasing the amount of resources allocated to the reserve block reduces the amount of resources that can be allocated to other access resources. Therefore, when sufficient resources are available in the containment-type resource and in the resource without containment, additional resources can be assigned to the reserve block. While the containment-type resource load and the resource without containment increases, the amount of resources allocated to the reserve block can be reduced. As noted above, the communication format used in the reservation block, the containment type access block and the non-containment access block do not need to be the same. A variety of well-known and further developed communication formats can be applied directly to the teachings of the invention. Normally, the non-containing access block and the containment-type access block use a common communication format and a channel to facilitate their instrumentation. For example, the containment-type access block can be assigned an amount of time and frequency segments and the non-containing access block can be assigned the time and the remaining frequency segments available in the system. Alternatively, or in combination, the containment-type access block can be assigned a first set of orthogonal codes for use in a broad-spectrum system while the non-containing access block can be assigned a series of remaining codes. In addition, frequency hopping techniques can also be used. However, it is likely that the reserve block operates according to some different communication format. An important feature of the reservation block is that it comprises a sufficient number of discrete resources so that each active remote unit can be assigned a single resource. It is also important that the delay in the transmission associated with the sending of a signal in the reservation resource is limited to a reasonable value. If the delay time associated with the successive transmissions from a single remote unit in the reserve block is too much, the delay may become transcendental to determine the delay associated with the retransmission in the block without containment. The invention can be incorporated into a variety of systems in which multiple units compete for access to a finite resource. Such systems include wireless terrestrial systems and wireline systems. In one embodiment, the non-containing access block may be used only after the information block has been subjected to one or more collisions in the contention-type access block. The invention can be incorporated into other specific forms without deviating from its spirit or essential characteristics. The described modality should be considered in all aspects only as illustrative and not limiting, and the scope of the claim of the invention is, therefore, indicated in the appended claims rather than in the previous descriptions. All the changes that are within the meaning and margin of equivalence of the claims will be considered as contents within their scope.

Claims (9)

1. In a communication system in which a plurality of remote units transmit to a central station, a communication method is composed of: The transmission of information blocks from one of said remote units to the central station The transmission of notification messages from the remote unit to the central station to notify the central station of the transmission of said information block; Which is characterized in that said information block is transmitted through a communication resource without containment and also because the central station, in response to receiving said notification message, determines whether the transmission of said block was carried out successfully of information through said containment-type communication resource; and transmits a response message from the central station to a remote unit ordering the latter to transmit said information block through a resource within a second access communication resource without containment in case it has not been carried out successfully transmitting said information block through said containment-type access communication resource, wherein said remote unit is configured to communicate together with said central station using a non-containing communication resource while other remote units of the system maintains its configuration to communicate with the central station using a containment communication resource.

2. The method of claim 1, wherein said response message designates said resource within said second communication resource without containment.

3. The method of claim 2, wherein the transmission of said information block further comprises the selection of an available resource from among a set of resource segments within said contention-type communication resource.

4. The method of claim 2, wherein said notification message indicates a first amount of information that is equal to a second amount of information of said information block.

5. The method of claim 2, wherein said notification message indicates a first amount of data of said information block.

6. The method of claim 2, wherein said resource within said non-containing access communication resource is of sufficient size to support the transmission of a difference between said first amount of information and a second amount of information received by said central station .

7. The method of claim 6, wherein said resource within said non-containment access communication resource is of sufficient size to support the transmission of said first amount of information.

8. The method of claim 6, further comprising transmitting an acknowledgment message from the central station to the remote unit ordering the remote unit to transmit any additional information available within a limited period through a resource within said remote unit. of access communication without containment.

9. A communication system comprising a plurality of remote units and a central station, wherein a subset of said remote units are configured to communicate together with said central station using an ALOHA communication resource and wherein at least one of said remote units is configured to communicate together with said central station using a first reserve communication resource, said remote unit being configured by said central station after sending a notification to said central station through a second reserve communication resource, said notification informing said central station of a data transfer from said remote unit to said central station through said ALOHA communication resource.