KR20090103988A - Communication systems - Google Patents

Abstract

PURPOSE: A communication system is provided to maximize spectrum efficiency and minimize delay by ensuring that a base station has no time in an idle state. CONSTITUTION: A communication method in a multi-hop wireless communication system comprises the steps of: providing first and second transmission windows to a wireless frame; transmitting data from an intermediate device by using a first transmission window, wherein the intermediate device corresponds to an odd hop from a base station device; and transmitting data from an intermediate device by using a second transmission window, wherein the intermediate device corresponds to an even hop from the base station device.

Description

Communication systems {COMMUNICATION SYSTEMS}

TECHNICAL FIELD The present invention relates to communication systems, and in particular, to the use of multihop techniques in packet-based wireless and other communication systems.

Recently, there is considerable interest in using multi-hop techniques in packet-based wireless and other communication systems, since such techniques will enable both an extension of coverage range and an increase in system capacity (throughput).

In a multi-hop communication system, communication signals are transmitted in a communication direction along a communication path C from the originating device to the destination device via one or more intermediate devices. 3 shows a base station BS (known as "Node-B (NB)" in the context of 3G communication systems), a relay node (RN) (known as a relay station RS), and a mobile station (MS). A single-cell two-hop wireless communication system having a user equipment (UE), also known as. When signals are transmitted from the base station to the destination user equipment UE via the relay node RN via the downlink DL, the base station means originating station S and the user equipment means destination station D. do. When communication signals are transmitted from the user equipment (UE) via the relay node to the base station via the uplink (UL), the user equipment means the calling station and the base station means the called station. The relay node is an example of an intermediate apparatus I and has a receiver operable to receive data from the originating apparatus and a transmitter operable to transmit this data or a derivative thereof to the destination apparatus.

Simple analog repeaters or digital repeaters have been used as relays to improve or provide coverage in dead spots. They can operate in a different transmission frequency band than the originating station or in the absence of transmission from the originating station in order to prevent interference between the originating station transmission and the repeater transmission.

4 illustrates a number of applications for relay stations. In the case of fixed infrastructure, the coverage provided by the relay station allows mobile stations that are unable to receive a signal of sufficient strength from the base station, even in the shadow of other objects or within the normal range of the base station, to access the communication network. It may be "in-fill". Also shown is a "range extension" which allows the relay station to access when the mobile station is outside the base station's normal data transmission range. One example of the infill shown at the top right of FIG. 4 is to deploy a nomadic relay station to allow for coverage extension in a building that may be located above, at, or below the ground.

Other applications are nomadic relay stations that provide access during an incident or emergency / disaster, resulting in a temporary cover effect. The last application, shown at the bottom right of FIG. 4, provides access to the network using a relay device deployed in the vehicle.

The relay devices may be used with advanced transmission techniques to improve the gain of the communication system, as described below.

As is known, in the case of wireless communication, scattering or absorption occurs as it travels through space, which results in propagation loss or "path loss", resulting in poor signal strength. Factors affecting path loss between the transmitter and receiver include transmitter antenna height, receiver antenna height, carrier frequency, clutter type (urban, suburban, rural), topographical details such as height, density, and separation. , Topography types (hills, flats). The path loss (L (dB)) between the transmitter and the receiver can be modeled by the following equation A,

Equation A

Where d (meter) is the isolation distance between the transmitter and the receiver, b (db) and n are the path loss parameters and the absolute path loss is given by l = 10 ^{(L / 10)} .

The sum of the absolute path losses experienced on the indirect link (SI + ID) may be less than the path losses experienced on the direct link (SD). In other words, the following equation B can be established.

Equation B

Thus, dividing a single transmission link into two shorter transmission segments uses a nonlinear relationship between path loss versus distance. From a simple theoretical analysis of path loss using Equation A, if a signal is not transmitted directly from the originating device to the destination device, but from the originating device to the destination device via an intermediate device (e.g., a relay node), It will be appreciated that a reduction in overall path loss (and thus an improvement or gain in signal strength and data throughput) can be realized. If implemented properly, multi-hop communication systems can reduce the level of interference as well as reduce exposure to electromagnetic radiation by enabling a reduction in the transmit power of transmitters that facilitate wireless transmission. Alternatively, the reduction in overall path loss can be used to improve the received signal quality at the receiver without increasing the overall radiated transmission power required for signal transmission.

Multi-hop systems are suitable for use by multi-carrier transmission. In a multi-carrier transmission system such as frequency division multiplex (FDM), orthogonal frequency division multiplex (OFDM), or discrete multi-tone (DMT), a single data stream has N parallel subcarriers, each with its own frequency range. Is modulated by As a result, the total bandwidth (that is, the amount of data to be transmitted in a predetermined time period) is divided over a plurality of subcarriers, thereby increasing the interval of each data symbol. Since each of the subcarriers has a lower information rate, multicarrier systems take advantage of improved resistance to distortion due to the channel compared to single carrier systems. This is accomplished by ensuring that the transmission rate and hence the bandwidth of each of the subcarriers is less than the coherent bandwidth of the channel. As a result, the channel distortion experienced by the subcarriers of the signal is frequency independent and can therefore be corrected by a simple phase and amplitude correction factor. As such, channel distortion correction entities in a multi-carrier receiver can be significantly less complex than those in a single carrier receiver if the system bandwidth exceeds the coherence bandwidth of the channel.

OFDM is a modulation technique based on FDM. An OFDM system can overlap without interference due to the fact that the spectra of subcarriers are independent of each other by using a plurality of subcarrier frequencies that are orthogonal from a mathematical point of view. Orthogonality of OFDM systems increases the spectral efficiency of the system by eliminating the need for guard band frequencies. OFDM has been proposed and adopted in many wireless systems. Currently, OFDM is used in Asymmetric Digital Subscriber Line (ADSL) connections, in some wireless LAN applications (such as WiFi devices based on the IEEE 802.11a / g standard), and in wireless MAN applications such as WiMAX (based on the IEEE 802.16 standard). This is used. OFDM is often used with channel coding and error correction techniques to generate coded orthogonal FDM (COFDM). COFDM is currently widely used in digital telecommunication systems to improve the performance of OFDM based systems in a multipath environment where variations in channel distortion can occur in both frequency carrier subcarriers and time domain symbols. The system has been used for certain types of computer networking technologies as well as video and audio broadcasts such as DVB and DAB.

In an OFDM system, N orthogonal blocks of N modulated parallel data transmission signals using an Inverse Discrete or Fast Fourier Transform algorithm (IDFT / IFFT) to form a signal known as an " OFDM symbol " in the time domain at the transmitter. To parallel subcarriers. As such, an "OFDM symbol" is a composite signal of all N subcarrier signals. OFDM symbol may be mathematically represented as the following equation (1),

Here, Δf is the subcarrier isolation distance in Hz, Ts = 1 / Δf is the symbol time period in seconds, and c _n is the modulated outgoing signals. The subcarrier vector (c ∈ C _n , c = (c ₀ , c ₁ ..c _N-1 )) in Equation 1 in which each of the outgoing signals is modulated is _N constrained from finite constellation. It is a vector of symbolization symbols. At the receiver, the received time domain signal is transformed back into the frequency domain by applying a Discrete Fourier Transform (DFT) or Fast Fourier Transform (FFT) algorithm.

Orthogonal Frequency Division Multiple Access (OFDMA) is a modified multiple access scheme of OFDM. It is effective by assigning a subset of subcarriers to individual users. This allows simultaneous transmission from several users, making the spectrum efficiency better. However, there is still a problem of enabling communication in both directions, i.e., uplink and download directions, without interference.

In order to enable bidirectional communication between two nodes, the two (forward or download and reverse or uplink) duplexed communication links so that the device cannot simultaneously transmit and receive over the same resource medium. There are two different known methods for overcoming the limitation. First, frequency division duplexing (FDD) requires operating the two links simultaneously but over different frequency bands by subdividing the transmission medium into two separate bands, one forward link communication and the other reverse link communication. Shall be. Secondly, time division duplexing (TDD) operates two links in the same frequency band, but at any point in time requires access to the transmission medium to be broken down in time such that only the forward or reverse link uses the medium. . Both methods (FDD & TDD) have their own relative advantages, all of which are widely used in single hop wired and wireless communication systems. For example, the IEEE 802.16 standard includes both FDD and TDD modes.

As an example, FIG. 5 illustrates a single hop TDD frame structure used in the OFDMA physical layer mode of the IEEE 802.16 standard (WiMAX).

Each frame is divided into a DL subframe and a UL subframe, each of which is a separate transmission interval. They are discrete by TTG (Transmit / Receive Transition Guard interval) and RTG (Receive / Transmit Transition Guard interval). Each DL subframe begins with a preamble followed by a Frame Control Header (FCH), DL-MAP, and UL-MAP.

The FCH includes a DL Frame Prefix (DLFP) for specifying the length and burst profile of the DL-MAP. The DLFP is a data structure transmitted at the beginning of each frame and contains information about the current frame, which is mapped to the FCH.

Concurrent DL assignments may be broadcast, multicast, and unicast, and they may also include assignments for other BSs than the serving BS. Concurrent ULs may be data allocations and range or bandwidth requests.

This patent application is the same applicant's agent reference numbers of P106752GB00, P106753GB00, P106754GB00, P106772GB00, P106773GB00, P106795GB00, P106796GB00, P106797GB00, P106798GB00, and P106799GB00, which describe the correlation inventions proposed by the inventors for the communication technologies. Is one of ten British patent applications filed on the same day by. The entire contents of each of the remaining nine applications are incorporated herein.

According to the present invention, it enables configuration of relay devices that include some local management of media access, and maximizes spectral efficiency by ensuring that the BS does not have any time in the frame when the BS is idle, thereby minimizing the minimum delay. A relaying enabled system can provide support for legacy single-hop TDD users, and the same transmission resources (frequency & time) using SDMA-based techniques allow the BS and RS and MS in the cell to By making it available between them, it further improves spectral efficiency, expands to any number of hops, defines specific synchronization intervals, enabling synchronization of the relay device with other relay devices or base stations, and RS A standard (similar to that sent by a BS) that can be decoded by a legacy user (which does not recognize any relay device). To enable transmitting or re-amble synchronization sequence.

1 illustrates a frame structure.

2 shows node activity within each zone.

3 illustrates a two-hop system.

4 shows applications of the relay.

5 illustrates a TDD frame structure used in OFDMA.

<Explanation of symbols for the main parts of the drawings>

B: broadcast zone

C: control transmission area

T: Data transfer transmission area

The invention is defined in the independent claims to be referred to below. Preferred embodiments are described in the dependent claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.

If a node is needed to support two independent links to two different nodes, for example, when the relay station is in communication with a base station and a mobile station, existing TDD or FDD frame structures may require some modification to realize a practical relay device. Is required.

Embodiments of the present invention provide a frame structure for a multi-hop communication system that is an extension of the standard TDD frame structure (see the IEEE 802.16 standard for an example) that provides support for any number of hops in the system. do. The proposed frame structure has many advantages as described later in this description.

The proposed frame structure assumes that the MS cannot reliably receive control information originating from the head node, or that the network comprising relay devices will perform some local connection management and / or medium allocation management. . This local management may be based on decisions made in some cooperation with the various nodes, either in the RS independent of all other nodes in the communication system or network, or including some control functionality. In addition, the RS has the ability to transmit control information, while all management decisions may be made at nodes other than the RS to which signals are transmitted.

The modified frame TDD structure also assumes that legacy mobile devices without relay station information should provide support for legacy mobile devices so that they can operate within a communication system or network.

1 shows a proposed general TDD frame structure.

This consists of multiple transmit and receive zones for both downlink and uplink subframes. Zone types are one of the following:

Broadcast of control related information such as synchronization sequences, commands, information, and details of the structure or layout of a B frame

Dedicated control information transmitted in the C non-broadcast zone (ie, individual receivers or groups of receivers)

T-only user-to-data transmission

Nine different zones are described in Table 1 below.

2 illustrates the operation of the BS, RS, and MS in terms of its activity within each of the zones described in Table 1. FIG.

2 illustrates only the case of a BS-RS1-RS2-RS3-MS link (ie, a 4-hop link), this frame structure can be used to support any number of hops. As shown for the case of RS3, the general concept is that the final relay device (RSn) in the hop transmits RP or RSn to RSn + 1 zones in the DL subframe or receives RSn + 1 as RSn in the uplink. It is not required to do so. Due to the fact that the RS transmits MAP information after receiving control information from the preceding transmitter (ie BS or RS), the two-hop relay will always cause at least one additional frame delay.

However, due to the fact that control information can be relayed from RS to RS within a frame, if more than two hops of relaying are taken, the proposed frame structure keeps relaying induced latency to a minimum. In this case, the delay is given by the following equation.

To enable implementation, the frame structure may have to include some gap times to allow the node to turn around (ie change from transmit mode to receive mode or vice versa). have. In this case, some of the zones may include a gap region or gap region that may be inserted between two adjacent regions that require a change in the node's operating mode.

If the BS is transmitting information to the RS in the MAP zone, it is more preferred that the BS first schedules the transmission to the RS before transmitting to any MS. The BS may then indicate when there is no longer pending information for the RS in the MAP zone, so that the BS may stop receiving while transmitting the MAP information to other receivers and stop this time. It can be used as an opportunity for turnaround.

The advantages of embodiments of the invention can be summarized as follows.

Enabling the configuration of relay devices that include some local management of media access.

Maximize spectral efficiency by ensuring that the BS does not have any time in the frame when the BS is idle.

Minimum Delay: 2-hop or 3-hop relay generates 1 frame delay, 4-hop or 5-hop relay causes 2 frame delay, and 6- or 7-hop relay generates 3 frame delay Let's do it.

A relaying enabled system makes it possible to provide support for legacy single-hop TDD users.

O There is a possibility to further improve spectral efficiency by making the same transmission resource (frequency & time) available between BS and RS and MS in the cell using SDMA based techniques.

Is scalable to any number of hops.

O Define a specific synchronization interval to enable synchronization of the relay device with other relay devices or base stations.

O allow the RS to transmit a standard preamble or synchronization sequence (similar to that sent by the BS) that can be decoded by a legacy user (which no relay device is aware of).

Embodiments of the invention may be implemented as hardware, or as software modules running on one or more processors, or a combination thereof. That is, those skilled in the art will appreciate that a microprocessor or digital signal processor (DSP) may be used substantially to implement some or all of the functionality of the transmitter implementing the present invention. In addition, the present invention may be embodied as one or more device or device programs (eg, computer programs and computer program products) for performing some or all of the methods described herein. Such programs embodying the present invention may be stored in computer readable media or may be, for example, in the form of one or more signals. Such signals may be data signals downloadable from an internet website, or may be provided via a carrier signal or in any other form.

Claims (12)

A communication method used in a multi-hop wireless communication system including a base station device, intermediate devices, and user equipment, the method comprising: Providing a first transmission window and a second transmission window in the radio frame; And Transmitting data from the intermediate apparatus corresponding to odd hops from the base station apparatus using the first transmission window and transmitting data from the intermediate apparatus corresponding to even hops from the base station apparatus using the second transmission window. Communication method comprising a. The method of claim 1, And the user equipment receives data from an intermediate device corresponding to the last hop. The method of claim 1, And the base station apparatus transmits data using the second transmission window to an intermediate apparatus corresponding to the first hop. The method of claim 1, The user equipment transmits data to an intermediate device corresponding to the last hop. The method of claim 1, And the base station apparatus receives data from the intermediate apparatus corresponding to the first hop using the first transmission window. The method of claim 1, And the intermediate apparatuses except for the base station apparatus and the intermediate apparatus corresponding to the last hop transmit a preamble, frame structure information, or relay amble using corresponding transmission windows. The method of claim 1, The intermediate apparatus corresponding to the last hop receives using the first transmission window or the second transmission window, but does not use the first transmission window and the second transmission window for transmission to the user equipment. The method of claim 1, A method of communication in which an intermediate device corresponding to the last hop does not transmit any relay amble. A multi-hop wireless communication system, Base station apparatus; Intermediate devices; And User equipment Including; A first transmission window and a second transmission window are provided in a radio frame, and an intermediate apparatus corresponding to an odd hop from the base station apparatus is configured to transmit data using the first transmission window and corresponds to an even hop from the base station apparatus. The intermediate apparatus is configured to transmit data using the second transmission window, Multi-hop wireless communication system. A base station device used in a multi-hop wireless communication system including intermediate devices, An intermediate device corresponding to an odd hop from the base station apparatus transmits data using a first transmission window of a radio frame, and an intermediate apparatus corresponding to an even hop from the base station apparatus uses a second transmission window of the radio frame. A transmitting unit, configured to transmit data to an intermediate apparatus corresponding to a first hop using the second transmission window of the radio frame when transmitting data Base station device comprising a. An intermediate apparatus used in a multi-hop wireless communication system including intermediate apparatuses, An intermediate device corresponding to an odd hop transmits data from the base station apparatus using the first transmission window of the radio frame, and an intermediate apparatus corresponding to an even hop from the base station apparatus uses the second transmission window of the radio frame. A transmission unit configured to transmit data using either the first transmission window or the second transmission window according to the number of hops from the base station apparatus to the intermediate apparatus when transmitting the? Intermediate device comprising a. A user equipment used in a multi-hop wireless communication system including intermediate devices, Either an intermediate apparatus corresponding to odd hops from the base station and transmitting data using the first transmission window of the radio frame or an intermediate apparatus corresponding to even hops from the base station and transmitting data using the second transmission window of the radio frame A receiving unit configured to receive data from one, wherein the intermediate apparatus for transmitting the data to be received by the receiving unit is an intermediate apparatus corresponding to the last hop; User equipment comprising a.