CN105978672A - Wireless ad hoc network based physical layer frame structure and configuration method thereof - Google Patents

Abstract

The invention discloses a configuration method for a physical layer frame structure based on an OFDM (Orthogonal Frequency Division Multiplexing) technology in a wireless ad hoc network. A frame formed by a preamble, a frame control head, a valid data segment and time-delay protection data which are mutually independent is generated, wherein the preamble comprises one or two OFDM symbols, the frame control head comprises one OFDM symbol, the valid data segment comprises an integer number of OFDM symbols and is composed of one or more bursts, and the time-delay protection data does not contain OFDM signals. The design of the frame structure can effectively relieve influences imposed on an OFDM communication system by noises, and improves the utilization rate of OFDM bandwidth at the same time, thereby improving the quality of wireless communication.

Description

A frame structure and configuration method based on physical layer of wireless ad hoc network

technical field

The invention relates to the field of wireless communication, in particular to a physical layer frame structure based on Orthogonal Frequency Division Multiplexing (OFDM) in a wireless ad hoc network.

Background technique

The traditional wireless cellular communication network requires fixed network equipment and base station support to perform data forwarding and user service control. The wireless self-organizing network MANET (Mobile Ad Hoc Network) does not require fixed equipment support, and each node, that is, a user terminal, can form a network by itself. During communication, other user nodes can serve as intermediate nodes for data forwarding. This form of network organization weakens the geographical limitations of traditional wireless networks to a certain extent, and its high-efficiency and convenient features are suitable for communication needs in some emergency situations, and occupy a very important position in military communications. However, wireless ad hoc networks also have disadvantages such as limited network bandwidth and low security.

In order to reduce the impact of disadvantages in wireless ad hoc networks on communication, Orthogonal Frequency Division Multiplexing (OFDM) has been widely used. Orthogonal frequency division multiplexing technology is to divide the channel into several orthogonal sub-channels, convert high-speed data signals into parallel low-speed sub-data streams, and modulate them for transmission on each sub-channel. Orthogonal signals can be separated by using correlation techniques at the receiving end, which can reduce the mutual interference ICI between sub-channels. The signal bandwidth on each sub-channel is smaller than the correlation bandwidth of the channel, so each sub-channel can be regarded as flat fading, so that the intersymbol interference can be eliminated. And since the bandwidth of each sub-channel is only a small part of the original channel bandwidth, channel equalization becomes relatively easy.

OFDM technology can send a large amount of data under narrow bandwidth, which is very helpful for limited bandwidth transmission in wireless ad hoc networks. At the same time, this technology can automatically detect which specific carrier has high signal attenuation or interference pulse under the transmission medium, and then take appropriate modulation measures to enable the carrier at the specified frequency to communicate successfully, which can solve the problem of wireless communication very well. The problem of channel interference in communication. However, although there are many advantages, OFDM technology also has certain defects. The entire OFDM system has extremely strict requirements on the orthogonality between subcarriers. Any small carrier frequency deviation will destroy the orthogonality between subcarriers and cause ICI. Therefore, OFDM systems are very sensitive to phase noise and carrier frequency offset. In addition, an OFDM signal consists of multiple subcarrier signals that are independently modulated by different modulation symbols. Compared with the traditional constant envelope modulation method, OFDM modulation has a very high crest factor. Because the OFDM signal is the sum of many small signals, the phase of these small signals is determined by the data sequence to be transmitted. For some data, these small signals may be in phase and add together in amplitude to produce large instantaneous peak amplitudes. If the peak-to-average ratio is too large, the complexity of A/D and D/A will be increased, and the efficiency of the RF power amplifier will be reduced. At the same time, at the transmitting end, the maximum output power of the amplifier limits the peak value of the signal, which will cause interference within the OFDM frequency band and between adjacent frequency bands.

In communications, a frame is a fixed or variable length packet of data encoded in accordance with a communication protocol for digital transmission. The frame structure defines the manner in which the multiplexer divides the communication channel into frames for transmission. The frame structure of an OFDM system has a major impact on the performance of the system. Currently, there are limited options for high-performance OFDM and OFDM frame structures. Therefore, it is necessary to provide a new frame structure design for high-performance OFDM systems to make up for the shortcomings of OFDM technology when it is applied to wireless communication.

Contents of the invention

Aiming at the shortcomings of OFDM in wireless communication in the above-mentioned prior art, the purpose of the present invention is to propose a frame structure and configuration method based on the physical layer of a wireless ad hoc network, which can effectively reduce the impact of phase noise on system communication. At the same time, the OFDM bandwidth can be effectively used to improve the quality of wireless communication.

A physical layer frame structure configuration method based on OFDM technology in a wireless ad hoc network, which is characterized in that a frame composed of mutually independent preamble, frame control header, valid data segment and delay protection data is generated;

The preamble includes 1 or 2 OFDM symbols, the frame control header includes 1 OFDM symbol, and the effective data segment includes an integer number of OFDM symbols, consisting of 1 or more bursts, the The delay protected data does not contain OFDM signals.

The time slot types are divided into node discovery segment, basic communication time slot and business communication time slot;

The node discovery segment includes 1 ms time slot and 2 ms time slot, the basic communication time slot is 1 ms time slot, and the business communication time slot includes 2 ms and 4 ms time slot.

The leading word includes two kinds of long leading and short leading;

The long preamble is composed of two OFDM symbols: the first OFDM symbol uses subcarriers whose number is a multiple of four, and the waveform in the time domain is composed of 4 repeated slices with a sampling value of 512. The front part has a cyclic prefix; the second OFDM symbol uses an even number of subcarriers, and its time domain structure consists of 2 repeated slices with a sampling value of 1024, with a cyclic prefix;

The short preamble occupies one OFDM symbol, and its time-domain structure consists of two repeated slices with a sampling value of 1024, with a cyclic prefix.

The length of the frame control header is an OFDM symbol, using BPSK modulation mode and 1/2 rate coding; the frame control header includes the specific modulation information of the entire data frame, wherein 3bit represents the modulation method, and 2bit represents the code length. The code rate occupies 2 bits, the number of OFDM symbols in the burst occupies 10 bits, and the header check sequence occupies 8 bits.

The effective data segment is composed of an integer number of OFDM symbols, and the duration of each symbol is 90 μs, and the number of selected bursts is determined by the channel property of the MAC layer. The length of the cyclic prefix is 10, and the length of the data is 80.

Compared with the prior art, the beneficial effect of the present invention is that the design of the frame structure can effectively alleviate the influence of phase noise on the OFDM communication system, and at the same time improve the utilization rate of OFDM bandwidth, thereby improving the quality of wireless communication.

Description of drawings

Fig. 1 is the frame structure schematic diagram based on wireless ad hoc network physical layer of the present invention;

Figure 2 is the time domain structure of the long preamble;

Figure 3 is the time domain structure of the short preamble;

Figure 4 shows the structure of the physical layer frame data part.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings.

1. Physical layer of wireless ad hoc network

The frame structure designed by the present invention is mainly aimed at wireless ad hoc networks based on OFDM technology. So the physical layer parameters of the wireless ad hoc network are particularly important for the design of the frame structure. The designed frame structure is designed for the basic parameters of the physical layer of the wireless ad hoc network, and can be well used for the transmission of data information of the physical layer.

2. Physical layer frame structure

2 is a schematic diagram of the frame structure based on the physical layer of the wireless ad hoc network in the present invention. With reference to the design of the MAC part, several frame structures after the physical layer is adapted to the MAC can be designed according to the specific parameters of the MAC layer.

The frame structure of the physical layer is mainly composed of four parts, namely: preamble, frame control header, valid data segment and delay protection data.

1. Preamble

There are two types of preambles—long preambles and short preambles.

The long preamble structure is shown in Figure 2, which consists of two OFDM symbols. The first OFDM symbol only uses subcarriers numbered in multiples of 4, and the waveform in the time domain is composed of 4 repeated slices with a sampling value of 512, and the front of the slice has a cyclic prefix (CP); Two OFDM symbols use only an even number of subcarriers, and its time-domain structure consists of two repeated slices with a sampling value of 1024, with a cyclic prefix.

The short preamble structure is shown in Figure 3. The short preamble occupies one OFDM symbol, and its time-domain structure consists of two repeated slices with a sampling value of 1024, with a cyclic prefix.

2. Frame control header

The length of the frame control header (FCH) part is one OFDM symbol. Use BPSK modulation and 1/2 rate coding. The information contained in the FCH is shown in Table 1:

Table 1 Specific information of frame control (FCH)

parameter name size (bit) Modulation 3 code length 2 code rate 2 Number of OFDM symbols in a burst 10 header check sequence 8

It can be seen from Table 1 that the rate domain filled in the information domain subband of the frame structure is composed of 7 bits, and the modulation mode and code of the data domain contained in the subband where the rate domain is located can be determined according to the information of these 7 bits. length and encoding rate. When the modulation mode is 001 and the code rate is 01, the modulation mode of the corresponding data field is BPSK, and the coding rate is 1/2, which is equivalent to 1 bit per subcarrier and one OFDM symbol per subcarrier. The number of data bits that can be transmitted per OFDM symbol is 1/2 bit; when the modulation mode is 001 and the code rate is 11, the modulation mode of the corresponding data field is BPSK, and the coding rate is 3/4, which is equivalent to each subcarrier The number of coded bits on each OFDM symbol is 1 bit, and the number of data bits that can be transmitted per OFDM symbol per subcarrier is 3/4 bits; when the modulation mode is 010 and the code rate is 01, the corresponding modulation mode of the data field It is QPSK, and the coding rate is 1/2, which means that the number of coded bits per OFDM symbol per subcarrier is 2 bits, and the number of data bits that can be transmitted per OFDM symbol per subcarrier is 1 bit; when the modulation mode is 100, the code When the rate is 10, the modulation method of the corresponding data domain is 64QAM, and the coding rate is 2/3, which is equivalent to 6 bits of coded bits per OFDM symbol per subcarrier, and the data that can be transmitted per OFDM symbol per subcarrier The number of bits is 4 bits.

3. Effective data segment

The frame structure of the valid data segment is shown in Figure 4. The valid data segment consists of an integer number of OFDM symbols, and the time of each symbol is 90 μs. The number of selected bursts is determined by the channel properties of the MAC layer. The length of CP is 10, and the length of data is 80.

3. Physical layer transmission process

The entire process of data frame transmission at the physical layer mainly includes: scrambling, multi-level rate coding and interleaving, modulation mapping, PN sequence generator, framing, upsampling and shaping filtering, etc.

1. Channel coding and modulation

This coding scheme is currently the coding scheme of LDPC. Contains 3 length encodings.

The specific codeword structure of LDPC encoding is that the information bit comes first and the parity bit follows. Take 1536 long codewords with a code rate of 1/2 as an example.

2. Interweave

Interleaving mainly completes two tasks: mapping between different LDPC modules; interleaving of different protection bits for high-level mapping.

3. Mapping

The mapping method adopts BPSK, QPSK (4QAM), 16QAM and 64QAM constellation diagrams.

4. Insert pilot

The pilots are inserted at equal intervals according to the frequency numbers of the pilot subcarriers of the physical layer of the wireless ad hoc network. It should be noted that the values of the guard subcarriers on both sides and the DC carrier are both 0. OFDM modulation

OFDM modulation process: First, the data undergoes serial-to-parallel conversion, then passes through IFFT, and finally outputs through parallel-to-serial conversion.

5. Add CP

After the pilot is inserted, it is the process of adding CP to the OFDM time domain transmission signal. An important reason for applying OFDM is that it can effectively combat multipath delay extension. In addition to eliminating inter-symbol interference through data parallel transmission, it is also necessary to insert a time guard interval between two consecutive OFDM symbols, which is generally implemented by using a cyclic prefix.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technology of the invention can be Modifications or equivalent replacements of the technical solutions without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the scope of the claims of the present invention.

Claims (5)

1. physical layer frame structure collocation method based on OFDM technology in a wireless self-organization network, it is characterised in that generate The frame being made up of separate preamble word, frame control head, valid data section and delay protection data；

Described preamble word includes 1 or 2 OFDM symbol, and described frame control head includes 1 OFDM symbol, described Valid data section includes integer OFDM symbol, is made up of one or more bursts, and described delay protection data do not comprise OFDM Signal.

Physical layer frame structure collocation method the most according to claim 1, it is characterised in that time slot kind is divided into node to send out Existing section, basic communication time slot and service communication time slot；

Described node finds that section includes 1ms time slot and 2ms time slot, and described basic communication time slot is 1ms time slot, described Service communication time slot includes 2ms and 4ms time slot.

Physical layer frame structure collocation method the most according to claim 1, it is characterised in that described preamble word includes long Leading and short leading two kinds；

Described long preambles is made up of two OFDM symbol: the subcarrier of the multiple of first OFDM symbol use numbered four, Waveform in time domain is 4 burst that sample value is 512 compositions repeated, and the front portion of burst is with Cyclic Prefix；Second OFDM symbol uses even number subcarrier, and its spatial structure is made up of 2 bursts that sample value is 1024 repeated, and with One Cyclic Prefix；

Described short leading taking 1 OFDM symbol, its spatial structure is made up of 2 bursts that sample value is 1024 repeated, And with a Cyclic Prefix.

Physical layer frame structure collocation method the most according to claim 1, it is characterised in that the length of described frame control head Degree is an OFDM symbol, uses BPSK modulation system and the coding of 1/2 speed；Frame control head includes whole Frame Concrete modulation intelligence, wherein 3bit represents that modulation system, 2bit represent that code length, code check account for 2bit length, the OFDM in burst Symbol numbers accounts for 10bit length, and head verification sequence accounts for 8bit length.

Physical layer frame structure collocation method the most according to claim 1, it is characterised in that described valid data section by Integer OFDM symbol forms, and each symbol time is 90 μ s, selects the number of burst to be determined by the channel properties of MAC layer. A length of the 10 of Cyclic Prefix, a length of the 80 of data.