MXPA06006997A - Handover in a wireless local area network (wlan) - Google Patents

Abstract

In triggering a handoff by a wireless transmit/receive unit (WTRU) from a current basic service set (BSS) in a wireless local area network (WLAN), the following are performed. A highest class of traffic service and quality of service (QoS) is determined for the highest class from a basic service set (BSS) beacon. Handoff is terminated and communication is retained with a current BSS when the signal to noise ratio (SNR) or received signal strength (RSS) is greater than a high threshold of the highest class. Other criteria is evaluated to determine whether a handoff is desired when the SNR or RSS is less than the high threshold.

Description

ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), For two-letler codes and other abbreviations, referto the "Guid-Éuropean (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, Fl, anee Notes on Codes andAbbreviations "appearing at the begin- FR, GB, GR, HU, IE, IS, IT, LT, LU, MC, NL, PL, PT, RO , no regular issue of the PCT Gazeite SE, SL SK, TR), OAPI (BF, BJ, CF, CG, Cl, CM, GA, GN, GQ, GW, ML, MR, NE, SN, TD, TG ). Published: without intemational search report and to be republished upon receipt ofthat repon TRANSFER IN A WIRELESS LOCAL AREA NETWORK (WLAN) FIELD OF THE INVENTION The present invention relates to wireless communication systems. In particular, the invention relates to switching in such systems.

BACKGROUND OF THE INVENTION Figure 1 is a simplified illustration of a wireless transmission / reception (WTRU) 14? N unit, which potentially switches between two basic service sets (BSSs), BSSi 12? and BSS2 122, in a wireless local area network (WLAN). Originally, BSS_ 12? has an access point (AP) 10? and a plurality of WTRUs 14u to 14_N and BSS2 122 have an access point (AP) 102 and a plurality of 'WTRUs 142i to 1423. The WTRU 14aN is in wireless communication with the AP 10_ .. As illustrated in the Figure 1, both APs 102, 10? they are connected to a distribution system 16. To decide whether to switch between BSSs 12, such as BSSi 12x and BSS2 122, WTRU 14_N measures the received signal strength (RSS) or the signal-to-noise ratio (SNR) for each BSS 12_, 122. The BSS 12 with the best RSS or SNR is selected for another communication. If BSSi 12_. Is selected, the current communication links are maintained, in accordance with the illustrated with a continuous line. If BSS2 122 is selected, a new link with BSS2 is established, as illustrated by a line of dashes. Although this approach most likely provides the WTRU 1 a_j with the most intense link, other criteria may make this connection inconvenient. For illustrative purposes, the BSS with the most intense link may be overloaded and may not meet certain quality of service (QoS) requirements of the WTRU 1 _.N. Accordingly, it is convenient to have alternative switching schemes.

THE INVENTION The following is carried out to trigger a switching by means of a wireless transmit / receive unit (WTRU) from a basic service set (BSS) current in a wireless local area network (WLAN) The highest class of traffic service and quality of service (QoS) is determined for the highest class from a basic service set beacon (BSS). Switching is terminated and communication with a current BSS is retained when the signal-to-noise ratio (SNR) or the received signal strength (RSS) is greater than a high threshold of the highest class. Other criteria are evaluated to determine if a switchover is convenient when the SNR or RSS is less than the high threshold.

BRIEF DESCRIPTION OF THE DRAWINGS An understanding of the present invention can be obtained from the consideration of the accompanying figures, where reference is made to similar elements through similar numbers, and where: Figure 1 is an illustration of a WTRU in Potential switching. Figure 2 is a flowchart of an RSS / SNR mode and another system statistics switching algorithm. Figure 3 is a simplified diagram of one mode of a WTRU capable of RSS / SNR and other switching of system statistics. Figure 4 is a flowchart of an RSS / SNR and another modality of system statistics switching algorithm. Figure 5 is a flowchart of a modality of an algorithm for calculating a QoS index, which can be employed by Figure 4.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used only (without the other features and elements of the preferred embodiments) or in various combinations with or without the other features and elements of the present invention. Next, a wireless transmit / receive unit (WTRU) includes but is not limited to a user equipment, station, mobile station, fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in an environment wireless When referenced below, an access point includes, but is not limited to, a base station, a Node B, a site controller, or any other type of interface device in a wireless environment. Although the following is discussed with respect to WLANs, the invention can be applied to other wireless networks. Figure 2 is a form of an RSS / SNR and another switching of system statistics. A WTRU, such as WTRU 14? N of FIG. 1, initiates the switching algorithm to determine whether a switching between BSSs 12 is desirable, such as from BSS_12_ to BSS2 122, step S30. The RSS AND / OR SNR is measured for each BSS 12, including the current BSS and any potential switching BSS, step S32. Other system statistics are measured for each BSS 12, step S34. The other system statistics may refer to the quality of service, such as delay limits, bandwidth requirements (ie, data rate), and frame error rate. Based on the RSS / SNR and other system statistics, a switching decision is made, step S36. Typically, the other system statistics are based on the traffic class of the WTRU services. Figure 3 is a mode of a WTRU 18 capable of said switching. The components of Figure 3 can be implemented in a single integrated circuit (IC), such as a specific application integrated circuit (ASIC), in multiple ICs, by means of discrete components or a combination of the IC or discrete components. The wireless signals are received and transmitted through an antenna 20 or antenna system and a transmitter / receiver (Xceiver) 22 of the WTRU 18. An RSS / SNR measuring device 24 measures the RSS and / or the SNR of each BSS 12. A switching controller 26 receives RSS / SNR measurements and other system statistics and determines whether a switch to another BSS 12 is convenient. The other system statistics can be retrieved from received communications, as shown in Figure 3 or by other means. Figure 4 is an illustration of a preferred embodiment for RSS / SNR and other switching of system statistics. For each traffic channel, QoS characters are defined, such as delay limits, bandwidth requirements (data rate), and frame error rate. Minimum and maximum values are defined for each parameter for each traffic class. A minimum and maximum value of SNR is also defined for each traffic class. Table -1 illustrates an example of QoS characteristics and SNR values for different traffic classes. Table 1: Characteristics of QoS and definition of SNR for different traffic classes The switching algorithm is triggered when the SNR value falls below a high SNR threshold, i.e., SNRmax, for the given traffic class (TC) associated with the entity seeking a switch, step S40. The CT may be one of those shown in Table 1. The algorithm compares the SNR value with a low SNR threshold and in accordance with the outcome acts, generally, as follows. If the SNR value is between the low and high SNR thresholds, the algorithm verifies the QoS index for this traffic class. The QoS index can be derived from any or all of the criteria in Table 1 or, alternatively, other criteria can be used. If the QoS index is below the QoS index threshold, the WTRU starts scanning neighboring cells to trigger a switch. If the SNR value is greater than the high SNR threshold, the algorithm ends because the link quality is good and there is no need for switching. For SNR values below the low threshold, the WTRU begins scanning neighboring BSSs without comparing the QoS index with the QoS index threshold. Although the above refers to SNR, RSS or a combination of RSS and SNR can be used instead. With reference to Figure 4, the highest class of service for traffic in the WTRU 18 that it monitors and the QoS requirements of the WTRU 18 are examined, step S42. If the SNR is at the low threshold or above it, step S44, the channel utilization and the frame loss rate are determined from the QBSS load element, step S48. The set QoS parameter element is verified, step S50, and the QoS index is calculated, step S52. If the QoS index is greater than a QoS index threshold, the switching algorithm is completed, steps S54, S86. If the QoS index is less than or equal to the threshold, the algorithm proceeds to determine a list of neighboring BSSs 12 to scan, as described subsequently, for steps S62 to S84. If the SNR is below the low threshold, step S44, the channel utilization and the frame loss rate derived from the QBSS load element, step S56 are determined. The set QoS parameter element is verified, step S58, and the QoS index is calculated, step S60. A list of neighboring BSSs 12 is determined, step S62, and a neighboring scan routine is started, step S64. The first BSS 12 in the list is scanned, step S66. The probe response is obtained from the first BSS 12 and the frame loss rate, the channel utilization and the QoS parameters are obtained from the probe response, step S68. The SNR and the QoS parameter elements are verified, step S70. A QoS index calculation is performed for the first BSS 12 of the neighbors to be scanned, step S72. In case there are more BSSs 12 in the list, step S74, the next BSS 12 is taken, step S76. Steps S68 to S74 are repeated for the following BSS 12. When there are no more BSSs 12 to be scanned, the BSS 12 with the highest QoS index is taken, in step S78. A difference is made between the QoS index of the selected BSS 12 and the QoS index of the current BSS 12. To prevent the WTRU 18 from frequently switching between the BSSs 12, the QoS index difference value is compared with a hysteresis, to determine if it is greater than the hysteresis, step S80. Hysteresis is preferably a function of the traffic class (TC), although it can be derived by other techniques. If the calculated difference is greater than the last stored hysteresis, the switching to the new cell is started and the hysteresis value is reset to its original value, step S82. The switching algorithm ends, step S86. If the difference between the QoS indices of the current cell and the target cell is less than the hysteresis, the hysteresis value is updated, step S84. Preferably, the hysteresis value decreases to allow the WTRU 18 to use the switching algorithm to have a better chance of obtaining a switch to a new cell, in case WTRU 18 continues to experience poor service. One embodiment of a QoS index calculation algorithm is shown in Figure 5. Although the algorithm can be used in other applications, it is preferably used with steps S52 and S72 of Figure 4. The QoS index is initially set to zero, steps S88, S90, and a list of available QoS parameters is created, step S92. The first QoS parameter in the list is selected, step S94. The selected QoS parameter is compared with the high threshold obtained from the associated traffic class (TC), step S96. If the selected parameter is greater than the high threshold, the QoS index is increased, step S98. Alternatively, if the QoS parameter is less than the high threshold and less than the low threshold, step S100, the QoS remains unchanged. If the QoS parameter is less than both the high threshold and the low threshold, the present QoS index is decreased by n + 1, where n is the total number of BSSs that are examined, step S102. After one of these three (3) steps, S90, S100, S102 has been carried out, it is determined if there are more QoS parameters to be examined, step S10. In case there are more QoS parameters, the next QoS parameter is selected, step S106. Steps S96 to S104 are repeated until all the QoS parameters have been examined. After all the QoS parameters have been evaluated, the QoS index is produced, step S108. Although Figure 5 is a mode for producing a QoS index, others can be used. For example, the QoS index can be produced by weighting QoS parameters. An application of the algorithms in Figures 4 and 5 can be with an AP and a WTRU that comply with 802. lie. Additionally, another application is with an AP and a WTRU 802.11b with the necessary parameters for the algorithm ag-watered to the beacon 802.11 and the response frames of probe b through proprietary signaling. These algorithms can also be applied to other wireless environments.

Claims (12)

1. CLAIMS 1. Method for determining a switching by means of a wireless transmission / reception unit (WTRU) from a basic service set (BSS) current in a wireless local area network (WLAN), characterized in that it comprises: determining a highest class of traffic service and quality of service (QoS) for the highest class from a basic service set beacon (BSS); obtain channel utilization and frame loss rate from the QBSS load element provided in the beacon; obtain the set of QoS parameters and the average delay in a current cell contained in the beacon; calculate the data using the QoS index that include one or more of: the channel utilization, frame loss and average delay in the BSS stream, and where the calculation of the QoS index also includes: a) establishing an index of QoS at zero (0); b) create a list of QoS parameters; c) select one of the QoS parameters; d) comparing the selected QoS parameter with a high threshold for such a QoS parameter; and e) carrying out one of increasing the QoS index when the selected QoS parameter is greater than the high threshold for such a QoS parameter; retaining a current QoS index when the selected QoS parameter is equal to the threshold for such a QoS parameter; and reduce the current QoS index. Method according to claim 1, characterized in that the current QoS index is reduced by (n + 1), where n is equal to a number of available QoS parameters. Method according to claim 1, further characterized by comprising: terminating a switch and maintaining communication with the current BSS when the QoS index is at least equal to the QoS index of the current BSS. 4. Method according to claim 1, further characterized in that it comprises: continuing a switching operation when the QoS index is lower than the QoS index of the current BSS. Method according to claim 4, characterized in that the continuation of the switching operation comprises: obtaining a list of neighboring BSSs; for each BSS in the list; obtain information from the selected BSS needed to calculate the QoS index; and initiating switching when the highest QoS index is greater than a hysteresis QoS threshold value. Method according to claim 5, further characterized in that it comprises: lowering the hysteresis QoS threshold to facilitate the subsequent switching procedures. 7. Wireless transmission / reception unit (WTRU) characterized in that it comprises: means to determine a higher class of traffic service and quality of service (QoS) for the highest class from a basic service set beacon (BSS) ); means for obtaining channel loss and frame loss rate from a QBSS loading element provided in the beacon; means for obtaining the setting of the QoS parameter and the average delay in a current cell contained in the beacon; means for calculating a QoS index using data including one or more of: channel utilization, delay and frame loss of the current BSS; and wherein calculating the QoS index also comprises a) establishing a QoS index at zero (0); b) create a list of QoS parameters; c) select one of the QoS parameters; d) comparing the selected QoS parameter with a high threshold for such a QoS parameter; and e) carrying out one of increasing the QoS index when the selected QoS parameter is greater than the high threshold for such a QoS parameter; retaining a current QoS index when the selected QoS parameter is equal to the threshold for such a QoS parameter; and reduce the current QoS index; and 'means for terminating a switch and retaining communication with the current BSS when the calculated QoS index is at hands equal to a QoS index threshold. 8. WTRU according to claim 7, characterized in that the current QoS index is reduced by (n + 1), where n is equal to a number of available QoS parameters. 9. WTRU according to claim 7, further characterized in that it comprises: means for terminating a switch and maintaining communication with the current BSS when the QoS index is at least equal to the QoS index of the current BSS. 10. WTRU according to claim 7, further characterized in that it comprises: means for continuing a switching operation when the QoS index is lower than the QoS index of the current BSS. 11. WTRU according to claim 10, characterized in that the continuation of the "-commutation operation comprises: obtaining a list of neighboring BSSs; for each BSS in the list; obtain information in a response mode from the selected BSS needed to calculate the QoS index; and initiating switching when the highest QoS index is greater than a hysteresis QoS threshold value. 12. WTRU according to claim 11, further characterized in that it comprises: means for lowering the hysteresis QoS threshold to facilitate the subsequent switching procedures.