Patent ID: 12192830

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receive unit (WTRU)” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. When referred to hereafter, the terminology “base station” includes but is not limited to an evolved Node-B (eNB), a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment.

The method and apparatus disclosed herein allows for an efficient usage of a dedicated preamble for handover performed by WTRUs in E-UTRA. The WTRU may use a dedicated preamble in pre-reserved (or preconfigured) frames, but not in every frame. Alternatively, the WTRU may use contention-based preambles in other random access opportunities when a dedicated preamble is not reserved.

Rather than reserving a dedicated preamble for a handover WTRU in every random access opportunity, (e.g., every 10 ms), the eNB will reserve a dedicated preamble N out of M random access opportunities, where the parameter M is defined as the period of a reserved dedicated preamble. A random access opportunity is a time period when a RACH may be accessed. In such an instance, the preferred value of Nis one.

As is shown inFIG.1, such a value facilitates the eNB to interleave several WTRUs sharing one dedicated preamble over the time domain. WTRU1only uses the dedicated preamble in a first random access opportunity out of every 4 random access opportunities. WTRU2only uses the dedicated preamble in a second random access opportunity out of every 4 random access opportunities. WTRU3only uses the dedicated preamble in a third random access opportunity out of every 8 random access opportunities. Thus, a dedicated preamble is efficiently shared by 3 WTRUs in the time domain.

The network will monitor and decide the value of parameters N and M based on the load on a non-contention RACH. Although different M values may be configured, a larger period must be an integer multiple of a smaller preamble period. In this way, WTRUs with different dedicated preamble configurations may share the same preamble without collision in the time domain. An example of a preferred set of a different reserved dedicated preamble periods is M=1, 2, 4 and 8.

FIG.2shows a wireless communication system200including a WTRU205and an eNB210. The eNB210reserves a dedicated preamble for a WTRU N out of M random access opportunities for a duration up to a maximum allowed handover interruption time. The eNB210may transmit reserved dedicated preamble configuration information215to the WTRU205via a handover command, when a handover decision is made, or via a special medium access control (MAC) protocol data unit (PDU). The WTRU205includes a transmitter225, a receiver230which receives preambles from the WTRU205, a processor235and a maximum handover interruption timer240. The eNB110includes a transmitter245, which is configured to transmit the reserved dedicated preamble configuration information215, a receiver250which receives the preambles from the WTRU205and a processor255. The processor255includes a preamble resource manager260, which is used to allocate preambles to the WTRU205.

The WTRU205transmits either a dedicated or contention-based preamble220to the eNB210such that the WTRU205can access a RACH to complete a handover procedure. If a RACH access attempt implemented by the WTRU205fails when using a dedicated preamble, the WTRU205will then use a contention-based preamble in subsequent random access opportunities until either its RACH access attempt succeeds or a random access opportunity occurs in which there is a reserved dedicated preamble.

Still referring toFIG.2, the WTRU200is configured to access a RACH during handover. The processor235is configured to initiate handover and activate the maximum handover interruption timer240. The transmitter is configured to transmit a dedicated preamble in an attempt to access the RACH on a condition that the dedicated preamble is reserved in a current random access opportunity and the maximum handover interruption timer has not expired, and transmit a contention-based preamble in an attempt to access the RACH on a condition that a dedicated preamble is not reserved in a current random access opportunity.

The transmitter225in the WTRU200is also configured to transmit a contention-based preamble in an attempt to access the RACH on a condition that the maximum handover interruption timer has expired. The transmitter225is also configured to transmit, on a condition that a failure to access a RACH has failed, a contention-based preamble in subsequent random access opportunities until a successful RACH access attempt occurs, or a random access opportunity occurs in which there is a reserved dedicated preamble.

A non-contention based procedure is used on a condition that the dedicated preamble is reserved in a current random access opportunity and the maximum handover interruption timer has not expired.

A contention-based random access procedure is used on a condition that the dedicated preamble is not reserved in a current random access opportunity and the maximum handover interruption timer has expired.

FIG.3is a flow diagram of a procedure300that uses a reserved dedicated preamble or a contention-based random access preamble during handover. Referring toFIGS.2and3, the processor235in the WTRU205initiates a handover to a target cell and activates the maximum handover interruption timer240in the WTRU205(305). When a random access opportunity occurs (310), a determination is made by the processor235as to whether the maximum handover interruption timer240has expired (315). If the maximum handover interruption timer240has not yet expired before a random access opportunity occurs, the processor235determines whether there is a dedicated preamble reserved in the current random access opportunity (step320).

If there is a reserved dedicated preamble in the current random access opportunity, the WTRU uses a dedicated preamble in random access, and a non-contention based random access procedure is used between the WTRU205and the eNB210to make a RACH access attempt (step325). A non-contention based random access procedure is two-step random access procedure that does not involve transmission of RACH message3in the uplink and contention resolution in the downlink, (as compared to a contention-based one).

If a reserved dedicated preamble does not exist in the current random access opportunity, the WTRU uses a contention-based preamble in random access, and a contention based random access procedure is used between the WTRU205and the eNB210to make a RACH access attempt (step330). A contention based random access procedure is a four-step random access procedure that involves transmission of RACH message3in the uplink and contention resolution in the downlink. The contention-based preamble may be randomly selected from a set of contention-based preambles.

In step335, a determination is made as to whether the RACH access attempt succeeded. If a WTRU fails its RACH access attempt using a reserved dedicated preamble, it will use a contention-based preamble in subsequent random access opportunities until either its RACH access attempt succeeds, or a random access opportunity occurs in which there is a reserved dedicated preamble.

Due to the high success probability of RACH access using a dedicated preamble, the approach to try a RACH access attempt with alternating non-contention based and contention based RACH access attempts is preamble resource efficient.

Although the features and elements of the present method and apparatus are described in particular combinations, each feature or element may be used alone, without other features and elements of the preferred embodiments, or in various combinations with or without other features and elements of the present method and apparatus.

While the present method and apparatus has been described in terms of the preferred embodiment, other variations which are within the scope of the invention will be apparent to those skilled in the art.

Although features and elements are described above in particular combinations, each feature or element may be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs).

Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine.

A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB) module.