WO2010000312A1

WO2010000312A1 - Apparatus for ranging, in particular for use in a multiple user multiple input multiple output wireless telecommunications network

Info

Publication number: WO2010000312A1
Application number: PCT/EP2008/058454
Authority: WO
Inventors: Hai Jiang; Jianfeng Kang; Shaohua Li
Original assignee: Nokia Siemens Networks Oy
Priority date: 2008-07-01
Filing date: 2008-07-01
Publication date: 2010-01-07

Abstract

The present invention relates to a method and apparatus, and in particular to an improved apparatus for use in a multiple user multiple input multiple output wireless telecommunications network. According to a first aspect there is provided an apparatus configured to generate a signal for combining with a code signal; and generate a further signal dependent on a combination of the code signal and the signal. Thus in embodiments it may be possible to reduce the probability of a code or ranging code signal collision between apparatus as the generated signal may enable a spatial orthogonality to be exploited. According to a second aspect there is provided an apparatus configured to: receive at least one signal from a further apparatus, wherein the further signal comprises a ranging code value; a ranging channel value; and an orthogonal vector value. According to a third aspect there is provided an apparatus configured to generate a precoding matrix for combining with a code signal; and generate a further signal dependent on a combination of the code signal and the precoding matrix

Description

APPARATUS FOR RANGING , IN PARTICULAR FOR USE IN A MULTI PLE USER MULTI PLE INPUT MULTIPLE OUTPUT WIRELESS TELECOMMUNICATIONS NETWORK

Field of the Invention

The present invention relates to a method and apparatus and, in particular but not exclusively, to an improved apparatus for use in a multiple user multiple input multiple output wireless telecommunications network.

Background

it has been proposed to improve the capacity of communication by use of spatial diversity or spatial multiplexing. By using spatial multiplexing, the data rate can be increased by transmitting independent information streams from different antennas but using the same channel as defined by frequency, time slot and/or spreading code.

These systems may be referred to as multiple input multiple output (M1M0) systems. These systems require complex controllers to control both the transmission and receiving elements of both the base station and the mobile station.

Multi-stream single user MIMO transmission has been proposed and forms part of WCDMA, 3GPP LTE and WiMax system standards. In order to receive multi-stream transmission, a MIMO receiver has to be applied in order to allow the separation and detection of the spatially multiplexed data streams using multiple antennas and receiving circuitry.

In contrast to single-user MIMO mentioned above, for multi-user (MU) MIMO, data streams are transmitted to several terminals in the same physical transmission resource by space division multiple access (SDMA). Multi-user MIMO is has been proposed to be part of future 3GPP LTE and WiMax standards. Recently, the IEEE 802.16 working group has established a new task group, 802,16m, to provide an advanced air interface which amends IEEE 802.16-2004 "IEEE Standard for Local and Metropolitan Area Networks - Part 16: Air Interface for Fixed Broadband Wireless Access Systems," published on Jun. 24, 2004, and 802.16e (also known as IEEE 802.16e-2005, "IEEE Standard for Local and Metropolitan Area Networks - Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems," published Feb. 28, 2006). One of the issues to be examined is that of Ranging. Ranging is one of the most important processes in the IEEE 802.16e standard, and include activities including initial ranging for network entry or handover ranging for re-entry, periodic ranging to maintain uplink synchronization and bandwidth request.

In 802.16e the initial ranging process is a contention-based procedure. The procedure specifies that a base station (BS) may allocate some time-frequency resources, i.e. ranging channels, to ail the users (user equipment (UE) or mobile stations (MS)) who request access to the base station. Each unsynchronized user equipment (UE) may, in order to communicate with the base station, randomly select and transmit a pseudo random (PN) code on the ranging channel. This enables the base station to recognize different user equipment from the different code used.

However there is a possibility that a collision will occur if two (or more) user equipment transmit to the base station using the same ranging code. The current contention resolution procedure is one within which at least one user equipment fails (by not receiving any acknowledgement of the original message) and the failed user equipment has to wait for another ranging opportunity to attempt to send the message again using a different ranging code. This causes the problem that there may be a significant delay in initial connection or in connection during handover as the ranging time is extended.

In the present standards such as 802.16e, the ranging code set contains only 256 codes, which are divided into 4 non-overlapping groups, with each group of codes assigned to a different purpose, i.e. initial ranging, periodic ranging, bandwidth request and handover ranging. One possible method for decreasing the collision probability and so prevent the delays is for the base station to allocate more time- frequency resources to ranging channels. This although reducing the probability of delays does so only by decreasing the available system spectrum availability for data transmission and thus reducing the system spectrum efficiency.

Thus conventional systems have to be designed with the trade off between increasing ranging opportunity and thus keeping ranging delays small and maintaining high spectrum efficiency and thus keeping data throughput high.

Summary

It is an aim of some embodiments of the present invention to address, or at least mitigate, some of these problems. In these embodiments of the invention, we propose a new method that could be used in multiple input multiple output communication systems which increases the ranging opportunity, reducing user equipment access time and bandwidth request time whilst not impacting significantly on the spectral allocation and thus impacting on the spectral efficiency of the system.

According to a first aspect of the present invention there is provided an apparatus configured to: generate a signal for combining with a code signal; and generate a further signal dependent on a combination of the code signai and the signal.

Thus in embodiments of the invention it may be possible to reduce the probability of a code or ranging code signal collision between apparatus as the generated signal may enable a spatial orthogonality to be exploited.

The apparatus may be further configured to generate the signal dependent on an estimate of a channel transfer function between the apparatus and a further apparatus. The apparatus may be further configured to: receive a downlink signal from the further apparatus; and estimate the channel transfer function between the apparatus and the further apparatus dependent on the downlink signal.

The apparatus may be further configured to: select one of a plurality of orthogonal vectors; and wherein the apparatus preferably is abie to generate the signal so that a combination of the estimate of a channel transfer function and the signal forms the one of a plurality of orthogonal vectors selected.

The apparatus may be further configured to generate the plurality of orthogonal vectors dependent on at least one of: a number of antennas in the apparatus; and a number of antennas in the further apparatus.

The apparatus may be further configured to select the code signal from a plurality of code signals.

The apparatus may be further configured to select the code signal from a plurality of code signals dependent on a number of antennas in the apparatus.

The code signal is preferably a ranging code.

The apparatus is preferably a user equipment.

The apparatus may be further configured to transmit the further signal to at least one further apparatus.

According to a second aspect of the invention there is provided an apparatus configured to: receive at least one signal from a further apparatus, wherein the further signal comprises: a ranging code value; a ranging channel value; and an orthogonal vector value. The apparatus is preferably configured to identify the further apparatus dependent on the combination of the ranging code value and the ranging channel value and the orthogonal vector vaiue.

The apparatus may be further configured to determine a number of antennas at the further apparatus dependent on the ranging code value.

The apparatus may be further configured to receive at least one further signal from at least one additional further apparatus, the at least one further signal may comprise: a further signal ranging code value; a further signal ranging channel value; and a further signal orthogonal vector value.

The apparatus is preferably configured to discriminate between the further apparatus and the at least one additional further apparatus dependent on a difference in at least one of: ranging code value; ranging channel value; and orthogonal vector value.

The apparatus may comprise a base station.

According to a third aspect of the invention there is provided an apparatus configured to: generate a precoding matrix for combining with a code signal; and generate a further signal dependent on a combination of the code signal and the precoding matrix.

The apparatus may be further configured to generate the precoding matrix dependent on an estimate of a channel transfer function between the apparatus and a further apparatus.

The apparatus may be further configured to: receive a downlink signal from the further apparatus; and estimate the channel transfer function between the apparatus and the further apparatus dependent on the downlink signal. The apparatus may be further configured to: select one of a plurality of orthogonal vectors; and wherein the apparatus is generate the precoding matrix so that a combination of the estimate of a channel transfer function and the precoding matrix forms the one of the plurality of orthogonal vectors selected according to the equation: r = H_{l UL} -P_t = Hf₀₁ - P₁ , where P is the precoding matrix, r is the one of the plurality of orthogonal vectors and HJ_,UL is the channel transfer function.

According to a fourth aspect of the invention there is provided a method comprising: generating a signal for combining with a code signal; and generating a further signal dependent on a combination of the code signal and the signal.

The method may further comprise generating the signal dependent on an estimate of a channel transfer function between an apparatus and a further apparatus.

The method may further comprise: receiving a downlink signal from the further apparatus; and estimating the channel transfer function between the apparatus and the further apparatus dependent on the downlink signal.

The method may further comprise: selecting one of a plurality of orthogonal vectors; wherein generating the signal may comprise generating the signal so that combining the estimate of the channel transfer function and the signal forms the one of a plurality of orthogonal vectors selected.

The method may further comprise generating the plurality . of orthogonal vectors dependent on at least one of: a number of antennas in the apparatus; and a number of antennas in the further apparatus.

The method may further comprise selecting the code signal from a plurality of code signals. The method may further comprise selecting the code signal from a plurality of code signals dependent on a number of antennas in an apparatus.

The code signal is preferably a ranging code.

The method is preferably performed in a user equipment.

The method may further comprise transmitting the further signal to at least one further apparatus.

According to a fifth aspect of the invention there is provided a method comprising: receiving at least one signal from an apparatus, wherein the further signal comprises: a ranging code value; a ranging channel value; and an orthogonal vector value.

The method may further comprise: identifying the apparatus dependent on the combination of the ranging code value and the ranging channel value and the orthogonal vector value.

The method may further comprise: determining a number of antennas at the apparatus dependent on the ranging code value.

The method may further comprise: receiving at least one further signal from at least one additional apparatus, the at least one further signal may comprise: a further signal ranging code value; a further signal ranging channel value; and a further signal orthogonal vector value.

The method may further comprise: discriminating between the apparatus and the at least one additional apparatus dependent on a difference in at ieast one of: ranging code value; ranging channel value; and orthogonal vector value. The method is preferably performed in a base station.

According to a sixth aspect of the invention there is provided a method comprising: generating a precoding matrix for combining with a code signal; and generating a further signal dependent on a combination of the code signal and the precoding matrix.

The method may further comprise generating the precoding matrix dependent on an estimate of a channel transfer function between an apparatus and a further apparatus.

The method may further comprise: selecting one of a plurality of orthogonal vectors; and generating the precoding matrix comprises generating the precoding matrix so that a combination of the estimate of the channel transfer function and the precoding matrix forms the one of the plurality of orthogonal vectors selected according to the equation: r =

-P₁ , where P is the precoding matrix, r is the one of the plurality of orthogonal vectors and H,,U_L is the channel transfer function.

An electronic device may comprise apparatus as described above.

A chipset may comprise apparatus as discussed above.

According to a seventh aspect of the invention there is provided a computer program product configured to perform a method comprising: generating a signal for combining with a code signal; and generating a further signal dependent on a combination of the code signal and the signal. According to an eighth aspect of the invention there is provided a computer program product configured to perform a method comprising: receiving at least one signal from an apparatus, wherein the further signal comprises: a ranging code value; a ranging channel value; and an orthogonal vector value.

According to a ninth aspect of the invention there is provided a computer program product configured to perform a method comprising generating a precoding matrix for combining with a code signal; and generating a further signal dependent on a combination of the code signal and the precoding matrix.

According to a tenth aspect of the invention there is provided an apparatus comprising: signal processing means for generating a signal for combining with a code signal; and further signal processing means for generating a further signal dependent on a combination of the code signal and the signal.

According to an eleventh aspect of the invention there is provided an apparatus comprising: processing means for receiving at least one signal from an apparatus, wherein the further signal comprises: a ranging code value; a ranging channel value; and an orthogonal vector value.

According to a twelfth aspect of the invention there is provided an apparatus comprising: processing means for generating a precoding matrix for combining with a code signal; and further processing means for generating a further signal dependent on a combination of the code signal and the precoding matrix.

Brief Description of the Drawings

The present invention is now described by way of example only with reference to the accompanying Figures, in which:- Figure 1 shows a schematic view of a system including an schematic base. station and user equipment configuration within which embodiments of the invention may be implemented;

Figure 2 shows a schematic view of an IEEE 802.16e time division duplex frame; Figure 3 shows a flow diagram of a method according to embodiments of the invention from the point of view of the user equipment; and Figure 4 shows a flow diagram of a method according to embodiments of the invention from the point of view of the base station.

Description of Exemplary Embodiments

Embodiments of the present invention are described herein by way of particular examples and specifically with reference to preferred embodiments. It will be understood by one skilled in the art that the invention may not be limited to the details of the specific embodiments given herein.

Figure 1 shows a communication network 30 in which some embodiments of the present invention may be implemented, in particular, some embodiments of the present invention may relate to the implementation of radio modems for a range of devices that may include: user equipment 201 , access points or base stations 101 which communicate over a wireless environment 151. Furthermore, embodiments of the present invention may be applicable to communication networks implemented according to a range of standards including: WCDMA (Wideband Code Division Multiple Access), 3GPP LTE (Long Term Evolution), WiMax (Worldwide interoperability for Microwave Access), UMB (Ultra Mobile Broadband), CDMA (Code Division Multiple Access), IxEV-DO (Evolution-Data Optimized), WLAN (Wireless Local Area Network), UWB (Ultra-Wide Band) receivers.

With respect to figure 1 , a schematic view of a system within which an embodiment of the invention may be implemented is shown. The communication system 30 is shown with a base station 101 which may be a node B (NB), an enhanced node B (eNB) or any access server suitable for enabling user equipment 201 to access wirelessly a communication system.

Figure 1 shows a system whereby the base station (BS) 101 may transmit to the user equipment (UE) 201 via the wireless environment communications channel 151 , which may be known as the downlink (DL), and the user equipment (UE) 201 may transmit to the base station (BS) 101 via the wireless environment communications channel 151 , which may be known as the uplink (UL).

The base station 101 can comprise a processor 105 which may be configured to control the operation of the receiver/transmitter circuitry 103. The processor may be configured to run software stored in memory 106.

The memory 106 may be further configured to store data to be transmitted and/or received. The memory 106 may further be used to store configuration parameters used by the processor 105 in operating the base station 101.

The transmitter/receiver circuitry 103 may be configured to operate as a configurable transmitter and/or receiver converting between radio frequency signals of a specific protocol for transmission over (or reception via) the wireless environment and baseband digital signals. The transmitter/receiver circuitry 103 may be configured to use the memory 106 as a buffer for data to be transmitted over or received from the wireless environment 151.

The transmitter/receiver circuitry 103 may further be configured to be connected to at least two antenna for receiving and transmitting the radio frequency signals over the wireless environment to the user equipment 201. In figure 1 the base station is shown comprising 2 antenna, the first antenna 107i and the second antenna 107₂ both configured to transmit and receive signals. In other embodiments of the invention the base station may have more antennas represented by the dotted antenna 107_m in figure 1. The base station 101 may be connected to other network elements via a communications link 111. The communications link 111 may receive data to be transmitted to the user equipment 201 via the downlink and transmits data received from the user equipment 201 via the uplink. This data may comprise data for all of the user equipment within the cell or wireless communications range operated by the base station 101. The communications link 111 is shown in figure 1 as a wired link. However it would be understood that the communications link may further be a wireless communications link.

In figure 1 , there is shown three user equipment 201 within the range of the base station 101. However it would be understood that there may be more or fewer user equipment 201 within range of the base station 101. The user equipment may be a mobile station, or any other apparatus or electronic device suitable for communication with the base station. For example in further embodiments of the invention the user equipment may be personal data organisers or laptop computers suitable for wireless communication in the environment as described hereafter.

Figure 1 in particular shows a first user equipment UEi 201₁, a second user equipment LJE₂201₂ and a KTH user equipment UE_κ201κ-

Furthermore figure 1 shows in more detail the first user equipment UEi 20I₁. The first user equipment 201₁ may comprise a processor 205 configured to control the operation of a receiver/transmitter circuitry 203. The processor may be configured to run software stored in memory 207. The processor may further control and operate any operation required to be carried out by the user equipment such as operation of the user equipment display, audio and/or video encoding and decoding in order to reduce spectrum usage, etc. However these additional operations are not described in any further detail and do not assist in the understanding of the operation of the invention. The memory 207 may be further configured to store data to be transmitted and/or received. The memory 207 may further be used to store configuration parameters used by the processor 205 in operating the user equipment 2011.

The transmitter/receiver circuitry 203 may be configured to operate as a configurable transmitter and/or receiver converting between radio frequency signals of a specific protocol for transmission over (or reception via) the wireless environment and baseband digital signals. The transmitter/receiver circuitry 203 may be configured to use the memory 207 as a buffer for data to be transmitted over or received from the wireless environment 151.

The transmitter/receiver circuitry 203 may further be configured to be connected to at least one antenna for receiving and transmitting the radio frequency signals over the wireless environment to the base station 101 , In figure 1 the user equipment is shown comprising 2 antennas, the first antenna 251 n and the second antenna 25112. In a first embodiment of the invention both the first 251 n and the second 25112 antenna may be used for receiving but only the first antenna 251 n may be configured to be used for transmitting. However it would be appreciated that in other embodiments of the invention different numbers of antennas may be connected to transmitter/receiver circuitry 203 and different numbers of antennas used for transmitting and receiving the signals over the wireless environment 151. For example in figure 1 the third user equipment 201 _k is shown with only one antenna 251 _ki configured to both transmit and receive signals.

Although figure 1 and the examples described hereafter describe the user equipment as having a processor arranged to carry out the operations described below, it would be understood that in embodiments of the invention the user equipment may comprise separate circuitry or processors configured to carry out separate processes. For example in some embodiments of the invention digital signal processors suitable for performing matrix and/or vector calculations may be used to perform the matrix calculations described hereafter. With respect to figures 2 to 4 examples of embodiments of the invention are shown in further detail. In the below examples we discuss the embodiments of a

Communications system between a base station employing two antennas with receive and transmit capability and a user equipment (the first user equipment 20I ₁) with two antennas capable of transmitting to the base station 101. It would be appreciated that in further embodiments of the invention other numbers of antennas may be employed. Furthermore in other embodiments of the invention there may be different numbers of user equipment and base stations capable of performing embodiments of the invention.

With respect to figure 2 a frame showing both the downlink (DL) and uplink (UL) components of a single IEEE 802.16e frame period is shown. The Frame 391 may have a period in a first embodiment of the invention of 5ms. The frame 391 may be divided into a downlink portion 351 where the base station 101 may transmit signals over a set of spectrum resources to the user equipment 201 , and an uplink portion 353 where the user equipment 201 may transmit signals over the spectrum resources to the base station 101.

The downlink portion 351 may comprise a preamble 301 which may be transmitted at the start of the frame and received by the user equipment.

The uplink portion 353 may comprise a ranging channel portion 307.

With respect to figure 3, an example of the present invention is shown with respect to the first user equipment UE2₀₁.

Firstly, the user equipment 201 may receive the downiink preamble as shown in figure 2 above. This receiving of the preamble is shown in figure 3 as step 401. The user equipment 201 may estimate the downlink channel state information (CSl) H_D ^k _L from the preamble information according to known channel state information estimation processes. Due to the time division duplexing of the channel the channel can be modelled as having characteristics both for the uplink and downlink which may be simply the inverse of each other. Thus the downlink channel state information may be used as an estimated uplink channel state information profile simply by carrying out a matrix transposition on the downlink channel state information matrix H_D ^k _L\o generate the estimated uplink channel state information. This may be represented in equation form by H_U ^k _L = [H_D ^k _L J

Where, [-f denotes the matrix transposition, and the superscript k denotes the k-th subcarrier. All of the mathematic operations may be dependent on their subcarriers, in other words the calculations may have to be made for each of the sub-carriers suitable for time division duplexing between the base station and user equipment. However for simplicity the superscript k is omitted in the following equations.

The step of estimating the downlink channel state information (CSI) from the preamble and the uplink channel state information from the downlink channel state information is shown in Figure 3 by step 403.

The user equipment 201 may then select a ranging code xi (where the sub-script value represents the user equipment and thus in this example the value xi is the ranging code selected by the first user equipment) from the set of ranging codes Xj. The selection may be made by a random or pseudo-random selection process from the set of ranging codes passed to the user equipment 201 from the base station or stored in the user equipment 201 previously. In other embodiments of the invention the ranging code X₁ for the first user equipment 2011 can be generated from a random or pseudorandom generator capable of generating a PN sequence of known length. In some embodiments of the invention the selection of the ranging code may be dependent on the number of transmitting antenna used for transmitting to the base station. In such embodiments of the invention the ranging codes may be partitioned into groups of codes associated with a number of transmitting antenna. This partition information may be received at the user equipment from the base station or may be generated in the user equipment by using predefined rules. For example in an embodiment of the invention the full set of ranging codes x may be partitioned into two groups of codes. The first set of n codes may be assigned to transmissions where 1 transmitter antenna is used X_tχ=i={x¹,...,xⁿ}, and the remainder m-n codes may be assigned to transmissions where 2 transmitter antennas are used

where m is the total number of ranging codes. The partition, in some embodiments, may be dynamically configured dependent on the number of user equipment and the distribution of user equipment transmitting antennas.

The selection/generation of the ranging code xi for the first user equipment 2011 is shown in figure 3 by step 405.

The user equipment may then select a precoding matrix P-|. The precoding matrix may be chosen in such a manner that possible collisions between the first user equipment 201₁ and a second user equipment 201₁ may be minimised.

To more easily explain the process of selection of the precoding matrix we can for this example use two user equipment each equipped with two transmit antennas, in such an example, the received signal matrix Y can be divided into the received signal vectors (yi y₂)^τ received on the base station first antenna 107-ι and the base station second antenna 107₂ which be modelled as

!U_,L ^{" P}2 ^{■ X}2 +

where H_{i UL} e C^2xl may be the uplink channel from the i'th user, xι and

P₁ = ^p_n P_{i 2}J may be the ranging code and precoding matrix of the i'th user, nj may be the thermal noise on the j'th receiver antenna, and i=1 ,2 (in other words there can be 2 user equipment) and j=1 ,2 (in other words there can be 2 receiver antennas).

If n can be made orthogonal to xi in other words r_x _L r₂ then the signal from two users can be separated at the base station receiver by the application of spatial processing, The values are n and r₂ may be any orthogonal vectors thus for example

Thus in a first embodiment of the invention the value of the precoding matrix may be generated by first selecting an orthogonal vector from a set of orthogonal vectors, for example the processor may select at random one of n or r₂ from one of the examples shown above, or randomly or pseudorandomly select one orthogonal vector from a set of orthogonal vectors.

This operation of selecting an orthogonal vector r_x from the set of orthogonal vectors r is shown in figure 3 by step 407.

The user equipment can calculate the precoding matrix required in order to orthogonalize the uplink channel by solving the following equation: r = H_IJϋL -P_l

-P₁

The operation of generating the precoding matrix Pi is shown in figure 3 by step 409. Therefore the apparatus may be considered to be configured to generate a signal, in the form of a precoding matrix signal for combining with a code signal, in the form of a ranging signal code; and may generate a further signal, in other words a modified ranging signal with the advantageous characteristics disclosed, dependent on a combination of the code signal and the signal.

The user equipment 201 may thus precode the uplink ranging code to generate a spatially separated signal and furthermore may indicate to the base station which precoding vector/matrix has been chosen together with which of the ranging vectors may have been chosen.

The precoding of the ranging vector and the signalling of the choices of the precoding and ranging vector are shown in figure 3 by step 411.

Thus in the embodiments of the invention the chances or probability of collision between ranging signals of any two user equipment at the base station may be reduced. In the above example the reduction of the probability of a collision may be by a factor of 2, as there are 2 possible selections of precoding vector. It would be understood that by using a higher number of dimensionality (for example the higher dimensions may be reached by increasing the rank of the CSI by increasing the number of transmitting and receiving antennas) the possibility of collision may be reduced further as the choice of codes may increase significantly.

With respect to Figure 4, the operation of the base station 101 and user equipment 201 is described in further detail with regards to embodiments of the invention.

The base station 101 processor 105 may, as shown in step 501 of figure 4, determine the resource for ranging and its location within the frame.

User equipment 201 in step 502 in the coverage of the base station 101 may send the ranging code on the given resource. The base station 101 in step 503 may receive the ranging codes from all of the user equipment 201 in coverage of the base station 101.

In the examples described previously the cell serviced by the base station 101 is likely to comprise a number of user equipment with single (IxTx) antenna configurations and a further number of user equipment with dual (2xTx) antenna configurations. In such an example the whole ranging code range may be shared by user equipment 201 in the range of the base station 101. The ranging code set S may be partitioned into two subsets, i.e., S1 (for IxTx configurations) and S2 (for 2xTx configurations), according to some algorithm. The partition may be predefined and known for the base station 101 and the user equipment 201 in the range of base station 101.

Then discrimination of ranging codes received may be improved over the prior art process in that for IxTx user equipment, the ranging codes received by the base station 101 may be discriminated within the processor 105 according to one of two possible discriminating variables { ranging channel, ranging code }. Furthermore for

2xTx user equipment (and for user equipment with more transmitting antennas in embodiments of the invention) the ranging codes received by the base station 101 may be discriminated within the processor 105 according to one of three possible discriminating variables { ranging channel, ranging code, (selected) orthogonal vector

}•

Therefore in an example where there are two possible user equipment (using the 1xTx and 2xTx configurations described above) attempting to access the system there may be three possible options.

Firstly if the two user equipment can be both equipped with IxTx antenna configurations then no collision may occur where the two user equipment select different ranging channels, or select different ranging codes. Secondly if one user equipment can be equipped with a IxTx antenna configuration, while another user equipment can be equipped with a 2xTx antenna configuration then collision may not occur, since the user equipment with the IxTx configuration may select a ranging code from the first set S1 or partition of ranging codes S, while the other user equipment with the 2xTx configuration may select a ranging code from the second set S2 or partition of ranging codes S. As the sets S1 and S2 can be non- overlapping partitions of the set S the codes selected by two user equipment may be different.

Thirdly if the two user equipment can be both equipped with a 2xTx antenna configuration a collision may not occur where the two user equipment can select different ranging channels, or the two user equipment can select different ranging codes, or the two user equipment can select different orthogonal vectors.

The advantages of these embodiments to summarize the above can be that by utilizing the TDD channel reciprocity and spatial orthogonality, the ranging opportunity may be increased (in the 2x2 example above by a factor of 2 and by a factor which may be dependent on the rank of the uplink/downlink channel model in general), without sacrificing spectrum efficiency and detection performance.

Thus the decreased collision probability in the ranging procedure and/or bandwidth request procedure, which are contention-based, may benefit users especially moving at the low to medium speed, in which the channel can vary slowly.

It is noted that whilst embodiments may have been described in relation to user equipment or mobile devices such as mobile terminals, embodiments of the present invention may be applicable to any other suitable type of apparatus suitable for communication via access systems. A mobile device may be configured to enable use of different access technologies, for example, based on an appropriate multi- radio implementation. [t is also noted that although certain embodiments may have been described above by way of example with reference to the exemplifying architectures of certain mobile networks and a wireless local area network, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein. It is also noted that the term access system may be understood to refer to any access system configured for enabling wireless communication for user accessing applications.

The above described operations may require data processing in the various entities. The data processing may be provided by means of one or more data processors. Similarly various entities described in the above embodiments may be implemented within a single or a plurality of data processing entities and/or data processors. Appropriately adapted computer program code product may be used for implementing the embodiments, when loaded to a computer. The program code product for providing the operation may be stored on and provided by means of a carrier medium such as a carrier disc, card or tape. A possibility may be to download the program code product via a data network. Implementation may be provided with appropriate software in a server.

For example the embodiments of the invention may be implemented as a chipset, in other words a series of integrated circuits communicating among each other. The chipset may comprise microprocessors arranged to run code, application specific integrated circuits (ASICs), or programmable digital signal processors for performing the operations described above.

Embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits can be by and large a highly automated process. Complex and powerful software tools may be available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate. Programs, such as those provided by Synopsys, Inc. of Mountain View, California and Cadence Design, of San Jose, California may automatically route conductors and locate components on a semiconductor chip using well established rules of design as well as libraries of pre-stored design modules. Once the design for a semiconductor circuit may have been completed, the resultant design, in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility or "fab" for fabrication.

It is 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 as defined in the appended claims.

Claims

1. An apparatus configured to: generate a signal for combining with a code signal; and generate a further signal dependent on a combination of the code signal and the signal.

2. The apparatus as claimed in claim 1 , further configured to generate the signal dependent on an estimate of a channel transfer function between the apparatus and a further apparatus.

3. The apparatus as claimed in claim 2, further configured to: receive a downlink signal from the further apparatus; and estimate the channel transfer function between the apparatus and the further apparatus dependent on the downlink signal.

4. The apparatus as claimed in claims 2 and 3, further configured to: select one of a plurality of orthogonal vectors; and wherein the apparatus is generate the signal so that a combination of the estimate of a channel transfer function and the signal forms the one of a plurality of orthogonal vectors selected.

5. The apparatus as claimed in claim 4, further configured to generate the plurality of orthogonal vectors dependent on at least one of: a number of antennas in the apparatus; and a number of antennas in the further apparatus.

6. The apparatus as claimed in claims 1 to 5, further configured to select the code signal from a plurality of code signals.

7. The apparatus as claimed in claim 6, further configured to select the code signal from a plurality of code signals dependent on a number of antennas in the apparatus.

8. The apparatus as claimed in claims 1 to 7, wherein the code signal is a ranging code.

9. The apparatus as claimed in claims 1 to 8, wherein the apparatus is a user equipment.

10. The apparatus as claimed in claims 1 to 9, further configured to transmit the further signal to at least one further apparatus.

11. An apparatus configured to: receive at least one signal from a further apparatus, wherein the further signal comprises: a ranging code value; a ranging channel value; and an orthogonal vector value.

12. The apparatus as claimed in claim 11 , wherein the apparatus is configured to identify the further apparatus dependent on the combination of the ranging code value and the ranging channel value and the orthogonal vector value.

13. The apparatus as claimed in claims 11 and 12, further configured to determine a number of antennas at the further apparatus dependent on the ranging code value.

14. The apparatus as claimed in claims 11 to 13, further configured to receive at least one further signal from at least one additional further apparatus, the at least one further signal comprising: a further signal ranging code value; a further signal ranging channel value; and a further signal orthogonal vector value.

15. The apparatus as claimed in claim 14, wherein the apparatus is configured to discriminate between the further apparatus and the at least one additional further apparatus dependent on a difference in at least one of: ranging code value; ranging channel value; and orthogonal vector value.

16. The apparatus as claimed in claims 11 to 15, wherein the apparatus comprises a base station.

17. An apparatus configured to: generate a precoding matrix for combining with a code signal; and generate a further signal dependent on a combination of the code signal and the precoding matrix.

18. The apparatus as claimed in claim 17, further configured to generate the precoding matrix dependent on an estimate of a channel transfer function between the apparatus and a further apparatus.

19. The apparatus as claimed in claim 18, further configured to: receive a downlink signal from the further apparatus; and estimate the channel transfer function between the apparatus and the further apparatus dependent on the downlink signal.

20. The apparatus as claimed in claims 18 and 19, further configured to: select one of a plurality of orthogonal vectors; and wherein the apparatus is generate the precoding matrix so that a combination of the estimate of a channel transfer function and the precoding matrix forms the one of the plurality of orthogonal vectors selected according to the equation:

where P is the precoding matrix, r is the one of the plurality of orthogonal vectors and H_Ϊ.U_L is the channel transfer function.

21. A method comprising: generating a signal for combining with a code signal; and generating a further signal dependent on a combination of the code signal and the signal.

22. The method as claimed in claim 21 , further comprising generating the signal dependent on an estimate of a channel transfer function between an apparatus and a further apparatus.

23. The method as claimed in claim 22, further comprising: receiving a downlink signal from the further apparatus; and estimating the channel transfer function between the apparatus and the further apparatus dependent on the downlink signal.

24. The method as claimed in claims 22 and 23, further comprising: selecting one of a plurality of orthogonal vectors; wherein generating the signal comprises generating the signal so that combining the estimate of the channel transfer function and the signal forms the one of a plurality of orthogonal vectors selected.

25. The method as claimed in claim 24, further comprising generating the plurality of orthogonal vectors dependent on at least one of: a number of antennas in the apparatus; and a number of antennas in the further apparatus.

26. The method as claimed in claims 21 to 25, further comprising selecting the code signal from a plurality of code signals.

27. The method as claimed in claim 26, further comprising selecting the code signal from a plurality of code signals dependent on a number of antennas in an apparatus.

28. The method as claimed in claims 21 to 27, wherein the code signal is a ranging code.

29. The method as claimed in claims 21 to 28, wherein the method is performed in a user equipment.

30. The method as claimed in claims 21 to 29, further comprising transmitting the further signal to at least one further apparatus.

31. A method comprising: receiving at least one signal from an apparatus, wherein the further signal comprises: a ranging code value; a ranging channel value; and an orthogonal vector value.

32. The method as claimed in claim 31 , further comprising: identifying the apparatus dependent on the combination of the ranging code value and the ranging channel value and the orthogonal vector value.

33. The method as claimed in claims 31 and 32, further comprising: determining a number of antennas at the apparatus dependent on the ranging code value.

34. The method as claimed in claims 31 to 33, further comprising: receiving at least one further signal from at least one additional apparatus, the at least one further signal comprising: a further signal ranging code value; a further signal ranging channel value; and a further signal orthogonal vector value.

35, The method as claimed in claim 34, further comprising: discriminating between the apparatus and the at least one additional apparatus dependent on a difference in at least one of: ranging code value; ranging channel value; and orthogonal vector value.

36. The method as claimed in claims 31 to 35, wherein the method is performed in a base station.

37. A method comprising: generating a precoding matrix for combining with a code signal; and generating a further signal dependent on a combination of the code signal and the precoding matrix,

38. The method as claimed in claim 37, further comprising generating the precoding matrix dependent on an estimate of a channel transfer function between an apparatus and a further apparatus.

39. The method as claimed in claim 38, further comprising: receiving a downlink signal from the further apparatus; and estimating the channel transfer function between the apparatus and the further apparatus dependent on the downlink signal.

40. The method as claimed in claims 38 and 39, further comprising: selecting one of a plurality of orthogonal vectors; and generating the precoding matrix comprises generating the precoding matrix so that a combination of the estimate of the channel transfer function and the precoding matrix forms the one of the plurality of orthogonal vectors selected according to the equation:

¹ S i where P is the precoding matrix, r is the one of the plurality of orthogonal vectors and HJ₁UL is the channel transfer function.

41. An electronic device comprising apparatus as claimed in claims 1 to 20.

42, A chipset comprising apparatus as claimed in claims 1 to 20.

43. A computer program product configured to perform a method comprising: generating a signal for combining with a code signal; and generating a further signal dependent on a combination of the code signal and the signal.

44. A computer program product configured to perform a method comprising: receiving at least one signa! from an apparatus, wherein the further signal comprises: a ranging code value; a ranging channel value; and a orthogonal vector value.

45. A computer program product configured to perform a method comprising: generating a precoding matrix for combining with a code signal; and generating a further signal dependent on a combination of the code signal and the precoding matrix.

46. An apparatus comprising: signal processing means for generating a signal for combining with a code signal; and further signal processing means for generating a further signal dependent on a combination of the code signal and the signal.

47. An apparatus comprising: processing means for receiving at least one signal from an apparatus, wherein the further signal comprises: a ranging code value; a ranging channel value; and a orthogonal vector value.

48. An apparatus comprising, processing means for generating a precoding matrix for combining with a code signal; and further processing means for generating a further signal dependent on a combination of the code signal and the precoding matrix.