SDR-Basic concept of future wireless communication equipment
According to the latest international developments, this article discusses and introduces software-defined radio (SDR). SDR is a new concept and system. It is a reprogrammable and reconfigurable wireless communication device that can support multiple wireless communication systems and standards. This article describes the US requirements for SDR equipment. This technology brings benefits to product development, manufacturers, operators, and end users, as well as the challenges faced by SDR. Obviously, in a few years, SDR technology will be widely used in the design of new generation wireless communication products, and wireless communication equipment based on SDR will become the main part of the market.
Abstract: Based on the latest internaTIonal development, this paper presents an in-depth discussion of the Software Defined Radio (SDR) technology. As a new concept or system, SDR is re-programmable and re-configurable, and capable of supporTIng radio communicaTIons equipment of mulTIple radio communications systems and standards. This paper shows what the US requires in the SDR equipment, the benefits brought along by this technology to product developers, manufacturers, operators and the ultimate users, as well as the challenges facing SDR. It is evident that in the next few years SDR will be widely applied in the designing of the new-generation radio communications products, and the SDR-based equipment will grow up to become a key element of the radio communications market.
Keywords: Software Defined Radio (SDR); advantages; challenges;
Key Words: Software Defined Radio (SDR); Advantage; Challenge
CLC number: TN929.5
Document identification code (Document code): A
Article ID (Article ID): 1009-9336 (2001) 04-0066-10
1 Introduction
In the author's previous article [1], the development direction of mobile communication technology was discussed and introduced. This article will focus on the most revolutionary software-defined radio technology.
As we all know, wireless communication technology has achieved unprecedented rapid development in the past 20 years. The advent of the 21st century, represented by the third generation of mobile communications, opened up a new world for the further development of wireless communications. Looking at the development of wireless communication technology over the past 20 years, you can see the following characteristics:
"Multiple access method from frequency division multiple access (FDMA) to time division multiple access (TDMA), and then to code division multiple access (CDMA);
"Each generation of technology is concentrated in the corresponding international standards, and the core of the standard is wireless transmission technology (RTT);
"Products are developed and produced according to a specific standard and provide specific services;
"The production of products all depends on special chips, and the technologies are all fixed in the special chips.
Through nearly 20 years of development, mobile communication has become the most active industry with the highest market share in the communications field, and has become the most competitive part of the international market.
However, this traditional idea and product development and production methods have shown many problems, such as:
"The product is developed and manufactured for a specific version of the standard. When new technologies appear or version upgrades or provide new services, new special chips can only be developed to manufacture a new generation of equipment. The result is not to limit new technologies And the use of new services is to bring greater investment risks to manufacturers and operators, and brings many inconveniences to users;
"With this traditional approach, it is inevitable to require global uniform standards, but it is difficult to achieve. Due to the economic interests of various countries, global uniform standards are almost impossible. On the contrary, the types of standards are still increasing. This causes frequency allocation and management. It is more difficult, the required frequency resources increase, the manufacturing of multi-frequency multi-mode handsets is difficult, and the cost increases, and it is unclear when the real global roaming can be implemented;
"Modern technology is progressing faster and faster. Before the third-generation mobile communication has been officially commercialized, ITU is already considering the issue of standard updating that has to be carried out due to technological progress. For the foregoing reasons, only the procedures for standard upgrading and updating are It is difficult to pass. This also affects the development and manufacturing of third-generation mobile communication devices to a certain extent, especially because of the progress of technology, the development of user terminals (mainly the development of dedicated chips) is slow, and the third-generation mobile The time for commercialization of communications was postponed.
Faced with this issue, internationally, mainly the United States, has conducted a lot of research. Typical is the conclusion of a research team of Massachusetts Institute of Technology (MIT) after consulting a large number of experts in wireless communication technology and industry: 77% of experts believe that "Software Defined Radio" (SDR) It is bound to be a solution to the global wireless communication needs. In 1999, the US FCC began to organize relevant experts to conduct research on SDR; in March 2000, it published a document [2], unifying the definition, requirements and related issues of SDR, and advocating the development of various companies and research institutions This technology. In the SDR forum, a lot of discussions and opinions were published [3], [4]. In October 2000, the US delegation took it as the development direction of mobile communication technology after the third generation, and submitted it to the ITU-R WP8F meeting and passed it [1].
The main purpose of this article is to introduce readers to this development direction of international mobile communication technology in the next period based on international discussions and publicly published information, and to provide reference for the decision-making of communication authorities, research and development departments, operators and manufacturers .
2 Definition and requirements of SDR
In the past few years, we often talked about software radio (Software Radio, referred to as SR), the concept of which is to achieve digital / analog (D / A) or analog / digital for the received signal or the signal to be transmitted as close as possible to the antenna (A / D) conversion, using software to realize the function of hardware through DSP, FPGA and other programmable devices. In a general sense, software radio is a means of implementing a specific wireless communication device.
The concept of SDR is much deeper, it is a concept of system and system. SDR's wireless communication device is considered a system, it must have the ability to be reprogrammed and reconfigurable, so that this device can be used in multiple modes (standards), multiple frequency bands and multiple functions. It not only uses programmable devices such as software radios to implement baseband digital signal processing, but also programs and reconstructs RF and IF analog circuits. SDR will be a revolutionary concept in the field of wireless communications.
At present, people have put forward the following functional requirements for wireless communication systems or devices using SDR:
1. The ability to reprogram and reset;
"SDR equipment can be quickly and easily reprogrammed and reset to support the application of any form of transmission and transmission or reception on any frequency;
"Reprogramming and resetting capabilities enable the same device to support different cellular technologies, personal communication systems, and other wireless services worldwide.
2. The ability to provide and change business
"Using SDR equipment, users can not only support traditional services but also support new services;
"The concept of downloading software over the air can ensure that users can get the latest business services.
3. Ability to support multiple standards
"SDR can better embody the concept of" interoperability "to support wireless communication systems that work in multiple frequency bands and multiple standards;
"In public safety and emergency handling departments, SDR technology is used to support multi-band communications;
"SDR enables wireless operators to achieve system version updates, standard updates, and upgrades without basically changing base station hardware. A new wireless communication system is defined through software.
4. Intelligent spectrum utilization
"SDR can improve spectrum utilization and frequency sharing, and can flexibly access to new frequency bands;
"SDR equipment has an" intelligent "function, it can monitor the spectrum used by other equipment, and transmit in the idle frequency band;
"SDR can greatly reduce the difficulty of frequency allocation and the risk of frequency allocation.
In general, SDR is a brand new concept and architecture that implements future mobile communication devices. It is not an isolated technology in itself, but a common platform for all new technologies.
3 Advantages brought by SDR
The use of the SDR concept to design and implement next-generation wireless communication systems and equipment has obvious advantages compared to traditional products and equipment. It will benefit everyone from technology research and development, to equipment manufacturers, to telecom operators, to every end user of wireless communications.
3.1 Research and development of technology and products
Traditional wireless communication systems only develop products for a single standard, from relatively stable standards to the design and development of dedicated chips, to product design and implementation, which is a year-by-year process with long development cycles and high development costs. The above situation resulted in that most of the new technologies could not be applied in the process of standard setting, which restricted the development and application of new technologies, resulting in a huge difference between commercial products and the technical level at that time.
SDR will provide a new concept and a universal wireless communication platform. On this platform, new services and new technologies may be implemented based on software, which greatly reduces development costs and cycles and enables products to keep up with the level of technological development.
In the future, new services will be developed by users. Only by using the concept of SDR can users be allowed to use SDR equipment to develop new services as they would use PCs.
3.2 For manufacturers
With the advancement of technology, the current life cycle of wireless communication products is getting shorter and shorter, so the investment risk for a single product line is very large. This requires mobile communication equipment manufacturers to have strong technical development and technical support capabilities, which greatly increases product costs. Even so, any failure in decision-making, management, or market will result in huge losses of investment.
SDR is product-based, and production based on SDR products will:
-Lower raw material cost than traditional products;
-Long product life means low investment risk;
-The product is easy to produce due to its simplified and standardized hardware.
Therefore, manufacturers producing products based on SDR technology can get much greater benefits than traditional products.
3.3 Operator
The construction of a mobile communication network requires huge investment and is also very risky. For example, on the one hand, due to market demand, China ’s GSM network is rapidly expanding and adding GPRS equipment; on the other hand, it is facing the upcoming period of third-generation mobile communications, and it is extremely difficult to formulate a successful investment strategy. In the next stage, we will consider how to choose among various standards of the third-generation mobile communication, which also has a great investment risk.
And products based on SDR technology will bring benefits to operators, it is manifested in:
-Lower cost than traditional products;
-Low investment risk, the same base station can currently work on the GSM network, can provide GPRS service through software upgrade, and then can work on any third-generation mobile communication standard
-The smooth transition in the true sense extends the life of system equipment;
-Provides a flexible and convenient hardware platform for providing new services.
Obviously, SDR will bring more profits to operators than traditional products.
3.4 For end users
Based on the SDR technology user's equipment, it is to provide users with a universal terminal equipment platform. It should be able to support up to 5 to 8 internationally accepted standards, and can achieve the purpose of upgrading user equipment through space loading software technology. Only in this way, the user does not need to care about the problems of his region and operator to realize the real world roaming. It is also possible for the user to obtain the new business he wants.
4 Challenges faced by SDR technology
At present, many international research units and companies are concerned about and researching SDR technology. But different companies still have different views on the future of SDR technology: most European companies think it will be widely used after 2008, some American companies think it may be widely used in 2005, and a few small high-tech companies are 2002-2003 launched the initial SDR wireless communication products (base stations and user terminals) and made efforts. In the end, what are the challenges in SDR technology and what are the key technical issues that have caused people to have such wide differences in the broad application prospects of this technology? This section will make a simple analysis of this.
4.1 System and structure
The SDR architecture should have the following characteristics:
-Flexibility: the possibility of handling multiple modes, multiple frequency bands, multiple standards, etc .;
-Upgradability: Must be compatible with existing major standards and have the ability to upgrade to standards that may be considered in the future;
-Scalability: There is the possibility of quantitative expansion in terms of equipment functions, services, capacity, etc .;
-Possibility of using future technology: This SDR device should use new technology that is currently being developed and may be applied in the future.
At present, people think that the architecture of SDR is a universal hardware platform. Its composition should include the basic units shown in Figure 1. The main units are explained below:
"Transceiver antenna and feeder: In order to use smart antenna technology, they should all be an antenna array composed of multiple antenna units. The radiation pattern will be controlled by baseband digital signal processing;
"RF transmitter: It consists of a common platform and multiple RF transmitter modules. Its operating frequency range should be wide enough and set with digital frequency synthesis technology. It should be able to work with multiple carriers for each standard. This transmitter also includes multiple High power amplifier. All transmitters should have high linearity, and techniques such as digital predistortion can be used to solve problems such as adaptive nonlinear compensation;
"RF receiver: It consists of a common platform and multiple RF receiver modules. Its operating frequency range should be wide enough and set with digital frequency synthesis technology. It should be able to work with multiple carriers for each standard;
"High-speed digital link: The link between the radio frequency and the baseband platform is multiple high-speed digital links. To support the second and third generation mobile communication standards, the digital signal transmission rate on this link will exceed 1 ~ 2Gbit The design of the / s bus structure is directly related to the success of the system;
"Universal baseband digital signal processing platform: This platform is composed of multiple same or different digital circuit boards, the number of which is determined according to the system capacity and can be expanded in a modular manner. In each circuit board, the main device is programmable , Configurable baseband digital signal processing circuit. This platform should complete several units on the right in Figure 1, such as interface, information application and control functions.
"Multiple software packages: After this platform is established, a large number of technologies and content are various software, which will include:
-Control software package: such as software for configuring, setting, and managing base stations;
-Physical layer software package: for each standard and standard, there will be its physical layer software;
-High-level software: separate for each standard and standard;
-System interface software: requirements for multiple interfaces.
These software will be stored in the baseband digital signal processing platform, or loaded through the network.
Figure 1 Basic unit of SDR structure
Figure 1 Basic Elements of the SDR Architecture
4.2 Broadband programmable and configurable RF and IF technology
In current wireless communication standards, the bandwidth of each carrier is from 25kHz (TACS) to 5MHz (WCDMA); the operating frequency band is from 800MHz to 3GHz; and there are different technical indicators in all aspects of radio frequency reception and transmission. This is the most challenging job for SDR multi-mode devices. The main problems are:
-Problems with broadband work. At present, the level of RF components can only support about 20% of the bandwidth, so in the initial SDR equipment, it may be required to replace the RF module when supporting multiple standards;
-Programmability and configurability of analog circuits. Analog circuits are the slowest part of technological progress, so when designing SDR equipment at present, the requirements for programming analog circuits are reduced as much as possible, and intermediate frequency (digital intermediate frequency) technology is widely used.
4.3 Smart antenna technology
For future wireless communication devices, especially base station devices, whether they work in TDD or FDD duplex mode, they must be based on smart antennas to provide higher spectrum efficiency. For SDR base station equipment, using smart antenna technology for all supported modes is also a challenge.
4.4 Baseband Processing Platform
From the technical core to the realization of programmable and configurable aspects, the core of any wireless communication standard is the physical layer technology in its RTT. With the advancement of technology, the complexity of digital signal processing technology is becoming higher and higher, which requires the ability of the baseband processing platform to become stronger and stronger. At present, the devices that can realize digital signal processing with software are mainly digital signal processor (DSP) and field programmable gate array (FPGA). The former has reached the capacity of thousands of MIPS; while the latter has exceeded one million doors. The above two devices have their own characteristics, and are suitable for handling different problems and algorithms. An important development direction is to combine the advantages of the two and use parallel processing technology to increase the processing capacity to tens of thousands of MIPS without infinitely increasing the main frequency. It also has the ability to quickly program and configure: the so-called "Super Parallel Processor" (Re-configurable Processor, RCP).
For user terminals, the baseband processing platform will mainly consist of MCU and RCP. In the terminal equipment, in addition to strong processing power, low power consumption is also required, which also depends on the progress of microelectronics in recent years to ensure.
4.5 Standard interface
For wireless base stations, different standards and systems have different network interfaces, such as Abis for GSM, Iub for 3GPP, and so on. The physical layer and the high layer are different. In SDR base stations, these different interface requirements must be supported and resolved through reprogramming and configuration.
4.6 Business issues
New services for user terminals can be provided by operators through space software loading, but the technology for space loading still needs to be improved; it is even more ideal for users to create the services they need, and there is still a long way to go.
5 Summary
This article gives a brief introduction to the recent international trends, mainly in the United States, in the face of the challenges of mobile communications development, in terms of software-defined radio (SDR) technology. The following conclusions can be drawn from the introduction of this article:
1. In terms of the implementation technology of wireless devices (base stations and user terminals), the most active is software-defined radio. It offers revolutionary prospects for the design and development of new generation products. After several years of hard work, the most competitive product in the wireless communication product market must be the concept of software-defined radio, with multi-mode base stations and user terminals. This direction of development has been very clear, the only unknown is when it appeared on the market.
2. The realization of software-defined radio must also overcome a large number of technical difficulties and establish a complete set of architecture. Relatively speaking, the difficulties in microelectronics and baseband digital signal processing are easier to overcome, while the difficulties in architecture and radio frequency technology are much greater. But in 1-2 years, we will see a breakthrough in this regard.
3. The TD-SCDMA wireless transmission technology standard proposed by our country is the only one that clearly design the smart antenna and high-speed digital modulation technology in the standard, and clearly implement the software radio technology. It can be said that TD-SCDMA technology represents the development direction of international mobile communication wireless transmission technology to a certain extent. On the other hand, TD-SCDMA technology is also more convenient to implement with software-defined radio.
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