WO2016119966A1

WO2016119966A1 - Method and apparatus

Info

Publication number: WO2016119966A1
Application number: PCT/EP2015/079527
Authority: WO
Inventors: Amaanat ALI; Kaustuv SAHA; Alexander Sayenko
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2015-01-30
Filing date: 2015-12-14
Publication date: 2016-08-04

Abstract

A method comprises determining in a device an initial power for transmission of a random access channel preamble from the device. The initial power is dependent on a constant. This constant can have a number of different values which can be used by the device. The random access channel preamble is transmitted with the determined initial transmission power.

Description

METHOD AND APPARATUS

Some embodiments relate to a method and apparatus and in particular but not exclusively to a method and apparatus for determining transmission power.

A communication system can be seen as a facility that enables communication sessions between two or more nodes such as fixed or mobile communication devices, access points such as nodes, base stations, servers, hosts, machine type servers, routers, and so on. A communication system and compatible communicating devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standards, specifications and related protocols can define the manner how communication devices shall communicate with the access points, how various aspects of the communications shall be implemented and how the devices and functionalities thereof shall be configured.

It should be understood that conveying, broadcasting, signalling, transmitting and/or receiving may herein mean preparing a data conveyance, broadcast, transmission and/or reception, preparing a message to be conveyed, broadcasted, signalled, transmitted and/or received, or physical transmission and/or reception itself, etc. on a case by case basis. The same principle may be applied to the terms transmission and reception as well.

A user can access the communication system by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE), user device or terminal.

Signals can be carried on wired or wireless carriers. Examples of wireless systems include public land mobile networks (PLMN), satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). Wireless systems can be divided into coverage areas referred to as cells, such systems being often referred to as cellular systems. A cell can be provided by a base station, there being various different types of base stations. Different types of cells can provide different features. For example, cells can have different shapes, sizes, functionalities and other characteristics. A cell is typically controlled by a control node. l A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communications with other parties. In wireless systems a communication device typically provides a transceiver station that can communicate with another communication device such as e.g. a base station and/or another user equipment. A communication device such as a user equipment (UE) may access a carrier provided by a base station, and transmit and/or receive on the carrier.

High speed packet access HSPA comprises the high speed downlink packet access protocol and the high speed uplink packet protocol which uses wideband code division multiple access WCDMA protocols. Evolved HSPA is defined in the 3GPP (third generation partnership project) specification.

According to an aspect, there is provided a method comprising: determining in a device an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms defining target signal to interference ratio information, said target signal to information ratio information having a plurality of possible values usable by said device; and causing the transmission of random access channel preamble with said determined initial transmission power.

The target signal to interference ratio information may comprise a constant. In the embodiments, mentioned below, reference is made to a constant. It should be appreciated that in other embodiments, any other target signal to interference ratio information may alternatively or additionally used.

The method may comprise determining if a response to said transmission is received and if not, increasing said determined initial transmission power by a power ramp step size value, said power ramp step size value being one of a plurality of power ramp step sizes.

According to a further aspect there is provided a method comprising: determining in a device an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms comprising a constant, said constant having a plurality of possible values usable by said device; and causing the transmission of random access channel preamble with said determined initial transmission power.

Said constant may be associated with a target signal to interference ratio. The method may comprise determining of at least one of a value of said constant target signal to interference ratio information and a value of said power ramp step size in said device.

The determining of at least one of a value of said constant and a value of said power ramp step size in said device may comprise using information used in previous successful access attempts by said device.

The determining of at least one of a value of said constant and a value of said power ramp step size in said device may comprise using a received value and modifying said received value.

The determining of at least one of a value of said constant and a value of said power ramp step size in said device may comprise selecting a higher of a received value and a lowest value previously used.

The method may comprise storing information on a value used in H previous access attempts.

The method may comprise receiving a value for at least one of said constant and a power ramp step size.

At least one of said constant and a power ramp step size may be dependent on a type traffic to be transmitted.

At least one of said constant and a power ramp step size may be dependent on a type of said device.

One of said terms may comprise a path loss term.

One of the terms may be an uplink interference term.

The device comprises a machine type communication device or a user device.

The method may be carried out by an apparatus. The apparatus may be provided in a device.

According to another aspect, there is provided a method comprising: determining at least one target signal to interference ratio information to be transmitted to a device, said target signal to interference ratio information having a plurality of possible values usable by said device, said target signal to interference ratio information being usable in said device to determine an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms comprising said target signal to interference ratio information. According to a further aspect, there is provided a method comprising: determining at least one constant to be transmitted to a device, said constant having a plurality of possible values usable by said device, said constant being usable in said device to determine an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms comprising said constant.

The method may comprise determining at least one power ramp step size value to be transmitted to said device, said power ramp step size value having a plurality of possible values usable by said device, one of said power ramp step sizes being usable by said device to determine a power for transmission of a further random access channel preamble.

The method may be performed by a control apparatus. The control apparatus may be provided in one or more of a base station, network control entity or any other suitable entity.

According to another aspect, there is provided an apparatus comprising: determining means for determining an initial power for transmission of a random access channel preamble in dependence on a plurality of terms, one of said terms defining target signal to interference ratio information, said target signal to information ratio information having a plurality of possible values usable by said device; and means for causing the transmission of random access channel preamble with said determined initial transmission power.

The target signal to interference ratio information may comprise a constant. According to a further aspect, there is provided an apparatus comprising: determining means for determining an initial power for transmission of a random access channel preamble in dependence on a plurality of terms, one of said terms defining a constant, said constant having a plurality of possible values usable by said device; and means for causing the transmission of random access channel preamble with said determined initial transmission power.

In the embodiments, mentioned below, reference is made to a constant. It should be appreciated that in other embodiments, any other target signal to interference ratio information may alternatively or additionally used.

The determining means may be for determining if a response to said transmission is received and if not, increasing said determined initial transmission power by a power ramp step size value, said power ramp step size value being one of a plurality of power ramp step sizes.

The determining means may be for determining at least one of a value of said constant target signal to interference ratio information and a value of said power ramp step size in said device.

The determining means may use information used in previous successful access attempts by said apparatus for determining at least one of a value of said constant and a value of said power ramp step size.

The determining means may use a received value and modify said received value for determining at least one of a value of said constant and a value of said power ramp step size.

The determining means may select a higher of a received value and a lowest value previously used for determining at least one of a value of said constant and a value of said power ramp step size.

The apparatus may comprise storing means for storing information on a value used in H previous access attempts.

The apparatus may comprise receiving means for receiving a value for at least one of said constant and a power ramp step size.

At least one of said constant and a power ramp step size may be is dependent on a type traffic to be transmitted.

One of said terms may comprise a path loss term.

One of the terms may be an uplink interference term.

The apparatus may be provided in a machine type communication device or a user device.

According to another aspect, there is provided an apparatus comprising: means for determining at least one target signal to interference ratio information to be transmitted to a device, said target signal to interference ratio information having a plurality of possible values usable by said device, said target signal to interference ratio information being usable in said device to determine an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms comprising said target signal to interference ratio information. According to a further aspect, there is provided an apparatus comprising: means for determining at least one constant to be transmitted to a device, said constant having a plurality of possible values usable by said device, said constant being usable in said device to determine an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms comprising said constant.

The determining means may be for determining at least one power ramp step size value to be transmitted to said device, said power ramp step size value having a plurality of possible values usable by said device, one of said power ramp step sizes being usable by said device to determine a power for transmission of a further random access channel preamble.

The apparatus may be provided in one or more of a base station, network control entity or any other suitable entity.

According to another aspect, there is provided an apparatus, said apparatus comprising at least one processor and at least one memory including computer code for one or more programs, the at least one memory and the computer code configured, with the at least one processor, to cause the apparatus at least to: determine an initial power for transmission of a random access channel preamble in dependence on a plurality of terms, one of said terms defining target signal to interference ratio information, said target signal to information ratio information having a plurality of possible values usable by said device; and cause the transmission of random access channel preamble with said determined initial transmission power.

The at least one memory and the computer code may be configured, with the at least one processor, to determine if a response to said transmission is received and if not, increase said determined initial transmission power by a power ramp step size value, said power ramp step size value being one of a plurality of power ramp step sizes.

The at least one memory and the computer code may be configured, with the at least one processor, to determine at least one of a value of said constant target signal to interference ratio information and a value of said power ramp step size in said device.

The at least one memory and the computer code may be configured, with the at least one processor, to determine at least one of a value of said constant and a value of said power ramp step size using information used in previous successful access attempts by said device.

The at least one memory and the computer code may be configured, with the at least one processor, to determine at least one of a value of said constant and a value of said power ramp step size using a received value and modify said received value.

The at least one memory and the computer code may be configured, with the at least one processor, to determine at least one of a value of said constant and a value of said power ramp step size by selecting a higher of a received value and a lowest value previously used.

The at least one memory and the computer code may be configured, with the at least one processor, to store information on a value used in H previous access attempts.

The at least one memory and the computer code may be configured, with the at least one processor, to receive a value for at least one of said constant and a power ramp step size.

One of said terms may comprise a path loss term.

One of the terms may be an uplink interference term.

According to another aspect, there is provided an apparatus, said apparatus comprising at least one processor and at least one memory including computer code for one or more programs, the at least one memory and the computer code configured, with the at least one processor, to cause the apparatus at least to: determine at least one target signal to interference ratio information to be transmitted to a device, said target signal to interference ratio information having a plurality of possible values usable by said device, said target signal to interference ratio information being usable in said device to determine an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms comprising said target signal to interference ratio information.

The at least one memory and the computer code may be configured, with the at least one processor, to determine at least one power ramp step size value to be transmitted to said device, said power ramp step size value having a plurality of possible values usable by said device, one of said power ramp step sizes being usable by said device to determine a power for transmission of a further random access channel preamble.

According to a further aspect there is provided an apparatus comprising at least one processor and at least one memory including computer code for one or more programs, the at least one memory and the computer code configured, with the at least one processor, to cause the apparatus at least to: determine an initial power for transmission of a random access channel preamble in dependence on a plurality of terms, one of said terms comprising a constant, said constant having a plurality of possible values usable by said device; and cause the transmission of random access channel preamble with said determined initial transmission power.

According to another aspect there is provided an apparatus comprising at least one processor and at least one memory including computer code for one or more programs, the at least one memory and the computer code configured, with the at least one processor, to cause the apparatus at least to: determine at least one constant to be transmitted to a device, said constant having a plurality of possible values usable by said device, said constant being usable in said device to determine an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms comprising said constant.

A computer program comprising program code means adapted to perform the method(s) may also be provided. The computer program may be stored and/or otherwise embodied by means of a carrier medium. In the above, many different embodiments have been described. It should be appreciated that further embodiments may be provided by the combination of any two or more of the embodiments described above.

Various other aspects and further embodiments are also described in the following detailed description and in the attached claims.

Some embodiments will now be described, by way of example only, with respect to the following Figures in which:

Figure 1 shows a schematic diagram of a network according to some embodiments;

Figure 2 shows a schematic diagram of a mobile communication device according to some embodiments;

Figure 3 shows a schematic diagram of a control apparatus according to some embodiments;

Figure 4 shows a first flow of current arrangements and modified in some embodiments; and

Figures 5 shows a second flow of some embodiments;

Figure 6 shows a signal flow of some embodiments; and

Figure 7 shows a third flow of some embodiments.

Before explaining in detail the exemplifying embodiments, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figures 1 to 3 to assist in understanding the technology underlying the described examples.

In a wireless communication system 100 mobile communication devices or user equipment (UE) 102, 104, 1 05 are provided wireless access via at least one base station or similar wireless transmitting and/or receiving node or point. Base stations are typically controlled by at least one appropriate controller apparatus, so as to enable operation thereof and management of mobile communication devices in communication with the base stations. The controller apparatus may be part of the base station and/or provided by a separate entity such as a radio network controller. In Figure 1 control apparatus 108 and 109 are shown to control the respective macro level base stations 106 and 107. The control apparatus of a base station can be interconnected with other control entities. The control apparatus and functions may be distributed between a plurality of control units. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller. In Figure 1 base stations 106 and 107 are shown as connected to a wider communications network 1 1 3 via gateway 1 1 2. A further gateway function may be provided to connect to another network. These may be macro base stations. The smaller base stations 1 16, 1 1 8 and 120 may also be connected to the network 1 13, for example by a separate gateway function and/or via the controllers of the macro level stations. In the example, stations 1 1 6 and 1 18 are connected via a gateway 1 1 1 whilst station 120 connects via the controller apparatus 108. In some embodiments, the smaller stations may not be provided. The smaller base stations may provide a femto cell, a pico cell, a micro cell, and/or the like.

A possible communication device will now be described in more detail with reference to Figure 2 showing a schematic, partially sectioned view of a communication device 200. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples include a mobile station (MS) or mobile device such as a mobile phone or what is known as a 'smart phone', a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, or any combinations of these or the like.

The device 200 may receive signals over an air or radio interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the device.

A device is typically provided with at least one data processing entity 201 , at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 204. The user may control the operation of the device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto. Some apparatus of the device may be configured to cause the performance of one or more of the signal flow steps as described later.

Figure 3 shows an example of a control apparatus 300. This control apparatus may be provided in one or more of a base station, a control entity or any other suitable entity. The control apparatus can be configured to provide control functions. For this purpose the control apparatus comprises at least one memory 301 , at least one data processing unit 302, 303 and an input/output interface 304. Via the interface the control apparatus can be coupled to receive and/or provide data. The control apparatus 300 can be configured to execute an appropriate software code to provide the control functions.

The HSPA technology has been a wireless broadband technology for some time and according to some forecasts it will remain so for a number of years. HSPA technology has been considered to provide a reasonable trade-off between efficiency and cost. HSPA technology as a potential technology for machine type communication (MTC) or machine to machine (M2M) devices.

Some embodiments may provide improvements for uplink enhancements for example improving the reception of a random access attempt and/or battery savings. The HSPA random access scheme may be considered to be a noticeable overhead in some situations. For example, the overhead may be considered to be relatively large where data plane volumes are marginal when compared to the amount of signalling traffic needed to establish the connection to the network.

It should be appreciated that this may be relevant for MTC devices. This may be relevant to some user devices. For example, this may be an issue for some user device applications.

Power ramping of the random access preamble is described in the 3GPP specification TS 25.331 and is described below.

Preamble_lnitial_Power = Primary CPICH TX power - CPICH_RSCP +

UL interference + constant value C

(Equation 1 ) Where

CPICH is the common pilot channel

RSCP is the received signal code power

UL is uplink

TX is transmission

In the above the constant values discussed may be used in the context of the equation 1 . It should be appreciated that equation 1 is by way of example only and the constant value may be used in any other suitable equation for determining a preamble initial power. It should be appreciated that the constant may be used as a multiplier or divider in some embodiments. In other embodiments the constant may be added to or subtracted from at least one other value. In other embodiments, instead of a constant, any other suitable term of an equation may be used.

The constant is an example of an offset/scaling factor that allows the system to balance between an initial transmission power (and as a result the average interference level) and how fast a UE will get a response. It should be appreciated that in other embodiments, any suitable way of defining, providing, selecting and/or determining of an offset/scaling factor may be used and embodiments are not limited to the use of a constant.

The preamble initial power is guided by the above equation where the difference between the first and second terms is the path loss. The third term is the UL rise over thermal (or UL load which is broadcast in a system information block (SIB) e.g. SIB7 on a periodic basis) and the fourth term is associated to an offset or scaling factor used for determination of the power for transmitting the random access preamble.

In this regard reference is made to the method shown in Figure 4 which shows a flow 500 according to a current procedure, and which may be modified in some embodiments. This flow may be performed in a user equipment or MTC device.

In step S502, the SIB is read from the system information message. This may be SIB5.

The PRACH (physical random access parameters) may comprise one or more of the following in the SIB:

modeSpecificlnfo fdd : {

primaryCPICH-TX-Power A, - the first term in the above equation constantValue C, the fourth term in the above equation

prach-PowerOffset {

powerRampStep B, step size for next attempt

preambleRetransMax D maximum number of attempts

},

It should appreciated that the values of A, B, C and D can have any suitable value.

In step S504, the key PRACH system information is read. A list of preamble signatures and a list of sub-channel numbers are stored.

In step S506, the PRACH partitioning information is read. The indicated number of partitions and the configuration for each partition is stored as access service class (ASC).

In step S508, the access class (AC) is mapped to the ASC. In this step, the PRACH partition corresponding to this ASC is retrieved.

In step S510, the RACH (random access channel) is initiated with a constant value from the retrieved PRACH partition.

In step 512, a UE determines the initial power for the preamble and in step S514 transmits the PRACH random access preamble with this power.

In step S51 6, the acquisition indication channel (AICH) is checked.

If there is no response, then the next step is step S520. In this step, the transmission of power is increased by a ramp up step size. If the UE receives no response on the AICH (i.e. a DTX discontinuous transmission), the UE would ramp up the preamble transmit power with a ramp step based on the SIB transmission. This is followed by step S514.

If a NACK (no acknowledgment) is received, then the next step is step S518 in which a back off procedure is performed. This is followed by step S512.

If an acknowledgement ACK is received, the next step is step S522 where the transmission continues with the message part of the transmission. Thus if there is an ACK on the AICH, the UE will continue transmitting the PRACH message part or may start using the common E-DCH (enhanced dedicated channel) resource.

The constant value is selected to a lower value in networks so that the device generally has to make at least two or three attempts before the device gets a RACH resource. This is to ensure that the devices do not choose a high initial power to start with which may impact the other real time traffic in the uplink. If during a data session a UE needs to send PRACH preamble just a few times, which is followed by a constant transmission over a common E-DCH in CELL FACH (forward access channel) state or over a dedicated resources in CELL DCH state, then the fact that a UE resorts to sending two or three PRACH attempts is not that significant. However, the inventors have appreciated that in case of marginal data volumes and/or when a UE moves from idle to connected state (whereupon each radio resource control (RRC) level signalling radio bearer (SRB) message would trigger a request for a new E-DCH resource), two or three PRACH attempts may create a noticeable overhead and may cause unnecessary delays.

Thus, in some embodiments, the constant value in the above equation may be tuned differently because of one or more of the following:

a MTC device has battery life constraints which may be far more stringent than that of high-end smart phones. Unsuccessful RACH attempts would waste battery power;

- a so-called optimal "constant value" may yield the highest uplink capacity; using such a value may help in compensating slow fading eventually resulting in a higher chance of successful preamble reception in the first attempt.

In the MTC scenario of some embodiments, there may be a trade-off between a reduction of UL capacity for existing traffic and a reduction of blocking probability (pb) for MTC devices, thus improving battery life. Both factors may in some embodiments be a function of the average number of retransmissions for successful RACH access and the access "power profile" which may be a function of the initial preamble power setting, the ramp-up step size and the max number of retransmissions. The probability of retransmissions (p_r ) may be a function of the access "power profile" as well as the probability of collisions (p_c>). This may be indirectly related to the average number of devices attempting to access the RACH within a cell. In the MTC scenario, the probability of collisions may be relatively large. In some embodiments, the average number of access devices per cell, in the MTC scenario, may be larger, as compared to a non-MTC scenario.

In the absence of collisions, the scenario wherein each RACH access attempt is successful on the first transmission may minimise the impact on the UL capacity of the cell for existing traffic. This may minimize the impact of p_r on p_c. Some

embodiments, provide a method which may be implemented in the UE to converge on this so-called optimum value. In some embodiments, a plurality of power ramp up step size values may be available. The power ramp up step value may be determined by the device. Alternatively, the power ramp up step value may be received in a transmission from the base station. In some embodiments, the power ramp up value may be determined by the device in dependence on information received in a transmission from the base station. The information may take any suitable form and in some embodiments may comprise an initial ramp up value. An initial C value is used and if this is unsuccessful (for example because no response is received) then the initial value of C may be increased by the step value.

Some embodiments may provide a plurality of C threshold values and/or power ramp step size values per PRACH preamble for determining the initial preamble power.

One or more C values or information on these one or more C values per PRACH preamble may be broadcast in system information.

One or more power ramp step size values or information on these one or more power ramp step size values per PRACH preamble may be broadcast in system information.

In some embodiments, one or more C values are computed by a UE or MTC device.

In some embodiments, the one or more C values are computed by a UE or

MTC device based on previous successful attempts.

In some embodiments, a UE selects a C value based on its device type (e.g. MTC capable).

In some embodiments, one or more power ramp step size values are computed by a UE or MTC device.

In some embodiments, the one or more power ramp step size values are computed by a UE or MTC device based on previous successful attempts.

In some embodiments, a UE selects a power ramp step size value based on its device type (e.g. MTC capable).

In some embodiments a UE selects/determines the C value and/or power ramp step size value based on the traffic type (e.g. only for common or dedicated control signalling, common or dedicated user plane traffic or for specific types of uplink application, or for delay sensitive application content, etc.). The cell can broadcast new PRACH parameters (for example in step S504 of Figure 4 guiding a UE to use different "C" values and/or power ramp step size values in different circumstances.

In some embodiments, the basic PRACH control information may be broadcast in SIB5, more specifically in IE information element -PRACH System Information List. Since SIB5 has an extension container, new parameters could be added for new UEs without breaking a compatibility with legacy UEs. However, it should be appreciated that in other embodiments, the information may be provided in any other SIB message or any other suitable message.

In an embodiment, a IE -PRACH preamble control parameters (for enhanced uplink) - may be provided which may be applied only to UEs supporting enhanced UL for CELL FACH. This is by way of example.

Information for some embodiments may alternatively or additionally be provided or determined which does not use the SIB5 mechanism.

A different "C" value may be applied to a particular traffic type, e.g. CCCH

(common control channel) and DCCH (dedicated control channel). This may be configured in the system information. This may allow the applying of more aggressive C values only for more critical and delay sensitive information, such as SRB data. This may be implemented in any suitable way, for example as an additional control IE in SIB5 or any other suitable message.

In some embodiments, the method of Figure 4 may be simply modified such that the received information in step S502 include the information set out previously, that is information relating to one or more of the constant C to be used and/or the step size.

Reference is made to the flow of 600 of Figure 5 which shows an embodiment.

Steps S602, S604, S606 and steps S608 respectively correspond to steps S502, S504, S506 and S508 of Figure 4.

In some embodiments, the RNC or other controller may decide to activate PRACH preamble optimizations and configure the system information accordingly.

In some embodiments, such as described in Figure 5, a different "C" value in equation 1 may be dynamically calculated by the UE with an algorithm which may use one or more of the following:

a. Absolute value of the UL RoT (third term in the equation). b. Current path loss measurement (first and second terms in equation 1 ).

c. Value of 'C broadcast in the SIB (CSIB). (this may be as discussed above) d. Past history of a number of successful access attempts by the UE.

The UE may maintain a history of the H most recent successful RACH access attempts, for example on a per-cell basis. H can be any suitable value. By way of example only, H may be between 10 and 20. However in other embodiments, H may be high than 20 or lower than 10.

In some embodiments, the history information may comprise weighting information. For example, most frequently used successfully and/or most recently used may be weighted more highly.

In some embodiments, a value of C may be associated with one or more other pieces of information. The information may indicate one or more of the type of traffic which was associated with the successful use of C, time information (for example the value of C which can be useful may be dependent on the time of day or day of the week), traffic conditions and/or the like.

For each record indexed with i (i = 1 , H), the UE stores the total number of transmissions n(i), and the value of C (C'(i)) for the final preamble transmission after which an ACK was received on the AICH.

C'(i) = C'o(i) + (n(i) - 1 )^*S', where C'o(i) is the initial value of C at the first preamble transmission, (n(i) - 1 ) = number of retransmissions and S' is the average ramp-up step size. C'(i) is a PRACH target SIR value which the UE is to dynamically compute for the current access attempt, to maximize the probability of a successful access attempt at the first transmission itself.

For the current access attempt, C'o(t) = max {CSIB, min value of C'(i) in H}. For the "first time" (no relevant history is available to the UE), and set C'o(t) = CSIB.

In step S61 0, it is determined whether or not history information is available.

If so, the next step is that S612 which initializes the algorithm with the history information.

If the there is no history available, then this is followed by step 614 which sets

In either case, the step S612 or step S614 are followed by step S61 6. In step S616, the preamble initial transmission power is estimated using the algorithm discussed previously. This is followed by step S618 which corresponds to step S514. Step S620 corresponds to step S516.

If a no acknowledgement NACK is received, a back off procedure is performed in step S624. This is followed by step S626, where the parameters are stored in the history information used in the algorithm.

If there is an acknowledgement ACK, the parameters will be stored in the history in step S628. This is followed by step S630 which continues with the message part of the transmission.

It should be appreciated that some embodiments, steps S628 and S630 may take place at the same time or in either order.

Retransmissions may still be required due to several reasons, e.g. UL and DL path losses may differ due to immediate radio conditions or due to mobility related reasons (in an MTC context, most of the devices may have limited mobility profiles), the access attempt could be triggered during a slow fade window that is negatively impacting the transmission, etc. In some embodiments, slow fading may be assumed to a major factor for retransmission, the power ramp-up step size S' = max{S'siB, min AC'(i) across all access attempts in H with n(i) > 1 , with respect to C'o(t)}. This is so that an approximate slow fade margin M from the access attempt history can be estimated and this may be used as the power ramp-up step size, so as to maximize the probability of successful access on the next retransmission. Thus if it is determined in step S620 that there is no response, in step S622, the next Tx power is estimated as described above.

Reference is made to Figure 7 which shows a modification to the method of Figure 5. Those steps which are the same are referenced by the same reference numbers.

Steps S602 to S608 are as described in relation to Figure 5. In step S614', the RACH access is initiated with a constant C value which is selected from a plurality of available values. This selection may take into account one or more other information. The information may be one or more of the type of device, the type of communication, network conditions and any other suitable conditions.

Steps S616 to S620 are as described in relation to Figure 5.

If there is no response found when checking the AICH, then the next step is step S622' in which a power ramp up step size from a list of available step values is selected. This selection may take into account one or more other information. The information may be one or more of the type of device, the type of communication, network conditions and any other suitable conditions.

If an ACK is present, then the next step is step S628 when the set of available values for the constant value is updated. For example in the constant value is updated after the application of a ramp up step, the updated constant value may be added to the available set of constant values.

If a NACK is present, then step S624 is followed by step S626' where the set of available values for the constant value is updated. For example in the constant value is updated after the back-off procedure, the updated constant value may be added to the available set of constant values. In other embodiments, the fact that the constant value has not been successful is noted. In those embodiments using history information, it can be determined if a particular constant value is not particular good or if the NACK was effectively unrelated to the value of the constant used. Some NACKs may be the result of unavailability of resources.

In other embodiments, step S626' may be omitted.

In some embodiments, an access attempt after a back-off may be regarded a new attempt which takes place after a back off period.

In some embodiments, the UE may determine the initial preamble power based on received and/or stored information.

In some embodiments, the UE may receive information from a base station which provides the initial preamble power or information from which the initial preamble power may be determined. Reference is made to Figure 6 which shows a signalling flow of an embodiment.

In this embodiment, the message flow is between a control apparatus, a base station and a user equipment. In this example, the control apparatus may be as shown in Figure 3. In some embodiments, the control apparatus may be provided in a RNC 108 or any other suitable entity. The base station may be any of the base stations shown in Figure 1 , for example base station 106. In some embodiments a base station may incorporate at least some of the functionality carried out by the control apparatus which in this example is provided by the base station.

The base station may be provided by a control apparatus such as that shown in Figure 3 for carrying out or causing the carrying out of one or more of the steps of Figure 6. It should be appreciated that there may be an interface between the control apparatus and base station to allow the entities to communicate. One example of a protocol to transmit control and user data between the entities may be NodeB Application Protocol (NBAP) of the 3GPP lub-interface. However, it should be appreciated that any other suitable protocol can be used and/or defined.

In step S60, the control apparatus 300, 1 08 may provide radio configuration parameters to a base station 106 which are needed to operate a cell of the base station 106. The radio configuration parameters may comprise one or more of:

one or more parameters relevant to the base station 106 for transmitting signals towards a UE and/or receiving signals from a UE; and

one or more parameters relevant to the user equipment UE 102 for receiving signals from the base station and/or for transmitting signals to the base station.

The control apparatus is responsible for providing corresponding parameters to the base station and the UEs within the coverage area of the base station to enable successful transmission and reception of signals. One or more radio configuration parameters are structured in system information blocks SIB and intended for any UE 102 within the coverage area of a base station 106. The control apparatus sends the radio configuration parameters as SIB to the connected base stations in step S60.

In step S61 , the base station 106 sends (for example by broadcasting) the one or more parameter to the UE. Those parameters may be relevant to UEs within the coverage of the base station in order to obtain access to a cell of the base station and exchange data afterwards. The base station may repeatedly transmits those SIB parameters as a broadcast message in step S61 . SIB5 and SIB7 are examples of those messages. The parameters may include one or more of the constant value(s) and/or the power ramp step size values.

The UE 102 receives in step S62 those SIB parameters and processes them as described for example, in relation to Figure 4 steps S500 - S512, Figure 5 steps S602 - S616 or Figure 7, steps S602 to S616. The UE may be in an idle state (e.g., 3GPP CELL FACH state) which means, there is no dedicated resource allocated to the UE for data transmission yet. An event occurs which requires a data transmission from the UE and triggers the random access procedure with the base station. The UE determines the initial transmission power for the PRACH preamble for example as described in relation to S512 or S61 6. In step S63, the UE sends a random access request towards the control apparatus /to the base station according to the SIB parameters received earlier and as described in relation to Figure 4 step S514, Figure 5 step S618 or Figure 7 step S618. Sending the random access request to the base station may comprise transmitting a PRACH preamble at a correct timing and with radio configuration parameters with which the base station expects random access requests.

In step S64, the UE expects a response from the base station to its access request and therefore observes the AICH which is related to the used random access channel and evaluates the received signal for an access confirmation. This is as described in relation to steps S620 of Figures 5 and 7 or step S516 of Figure 4.When the base station does not detect a random access request, no response or confirmation will be send to the UE on the AICH. If the UE did not detect or receive a random access confirmation, the optional step S65 is executed in which the preamble power of the next random access request is determined. This may be as described in relation to Figure 4 step S520, Figure 5 step S622 or Figure 7 step 622'.

In step S66 another access request is transmitted to the base station, for example as described in relation to Figure 4 step S514, Figure 5 step S618 or Figure 7 step S618.

In step S67, the UE expects a response from the base station to its access request similar to step S64 and evaluates the received signal for an access confirmation (e.g. for an ACK).

When the base station successfully detects and decodes a random access request, the base station sends a confirmation of successful receipt to the UE on the AICH as shown in step S68. Once the UE receives and detects the access confirmation in the AICH, the UE proceeds in step S69 to transmit the data part of the random access request to the base station.

The base station forwards in step S70 the received data and further information of the random access of the UE to the control apparatus for further processing and evaluation of the access request.

Some embodiments may provide an algorithm or computer program which may be run by an apparatus in the device. The apparatus may comprise at least one processor and at least one memory. The computer program, may, when run chose one of a plurality of possible constant values and/or power ramp step size values. Some embodiments may be such that the network may send to the device one or more constant values and/or power ramp step size values. For example, a plurality of constant values and/or power ramp step size values are available and the network may send one of those values. In other embodiments, more than one constant value and/or power ramp step size value may be sent. The one or more constant values and/or power ramp step size values may be included in a SIB message. The SIB message may be a SIB5 message. When the network sends a plurality of constant values and/or power ramp step size values, RRC specification may include the plurality of constant values and/or power ramp step size values. This may be achieved by using more than one IE for the constant values and/or power ramp step size values.

In one of the embodiments, the SIB5/5bis may carry a plurality of constant values and/or power ramp step size values for the device to choose from.

In some embodiments the plurality of constant values and/or power ramp step size values may be determined in the network. The values may be determined by a base station, a controller such as a RNC or by cooperation there between.

In some embodiments, the UE may arrive at the plurality of constant values and/or power ramp step size values based on storing past samples in one or more memories. The one or more memories may comprise one or more buffers.

An appropriately adapted computer program code product or products may be used for implementing the embodiments, when loaded on an appropriate data processing apparatus. The program code product for providing the operation may be stored on, provided and embodied by means of an appropriate carrier medium. An appropriate computer program can be embodied on a computer readable record medium. A possibility is to download the program code product via a data network. In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Embodiments of the inventions may thus be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

It is also noted herein that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

Claims

Claims:

1 . A method comprising:

determining in a device an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms comprising a constant, said constant having a plurality of possible values usable by said device; and

causing the transmission of random access channel preamble with said determined initial transmission power.

2. A method as claimed in claim 1 , wherein said constant is associated with a target signal to interference ratio.

3. A method as claimed in claim 1 or 2, comprising determining if a response to said transmission is received and if not, increasing said determined initial transmission power by a power ramp step size value, said power ramp step size value being one of a plurality of power ramp step sizes.

4. A method as claimed in claim 3, comprising determining of at least one of a value of said constant and a value of said power ramp step size in said device.

5. A method as claimed in claim 4, wherein said determining of at least one of a value of said constant and a value of said power ramp step size in said device comprises using information used in previous successful access attempts by said device.

6. A method as claimed in claim 4 or 5, wherein said determining of at least one of a value of said constant and a value of said power ramp step size in said device comprises using a received value and modifying said received value.

7. A method as claimed in claim 4, 5 or 6, wherein said determining of at least one of a value of said constant and a value of said power ramp step size in said device comprises selecting a higher of a received value and a lowest value previously used.

8. A method as claimed in any previous claim, comprising storing information on a value used in H previous access attempts.

9. A method as claimed in claim 3, comprising receiving a value for at least one of said constant and a power ramp step size.

10. A method as claimed in claim 3, wherein at least one of said constant and a power ramp step size is dependent on a type traffic to be transmitted.

1 1 . A method as claimed in claim 3, wherein at least one of said constant and a power ramp step size is dependent on a type of said device.

12. A method as claimed in any preceding claim where one of said terms comprises a path loss term.

13. A method as claimed in any preceding claim, wherein one of the terms is an uplink interference term.

14. A method as claimed in any preceding claim, wherein said device comprises a machine type communication device or a user device.

15. A method comprising:

determining at least one constant to be transmitted to a device, said constant having a plurality of possible values usable by said device, said constant being usable in said device to determine an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms comprising said constant.

16. A method as claimed in claim 1 5, comprising determining at least one power ramp step size value to be transmitted to said device, said power ramp step size value having a plurality of possible values usable by said device, one of said power ramp step sizes being usable by said device to determine a power for transmission of a further random access channel preamble.

17. An apparatus comprising at least one processor and at least one memory including computer code for one or more programs, the at least one memory and the computer code configured, with the at least one processor, to cause the apparatus at least to:

determine an initial power for transmission of a random access channel preamble in dependence on a plurality of terms, one of said terms comprising a constant, said constant having a plurality of possible values usable by said device; and

cause the transmission of random access channel preamble with said determined initial transmission power.

18. An apparatus comprising at least one processor and at least one memory including computer code for one or more programs, the at least one memory and the computer code configured, with the at least one processor, to cause the apparatus at least to:

determine at least one constant to be transmitted to a device, said constant having a plurality of possible values usable by said device, said constant being usable in said device to determine an initial power for transmission of a random access channel preamble from the device in dependence on a plurality of terms, one of said terms comprising said constant.

19. A computer program product comprising a plurality of computer executable instructions which when run cause the method of any of claims 1 to 16 to be performed.