What is a Cordless Phone?

In 1993, Siemens developed the world's first digital cordless telephone. In the same year, Siemens established the "Gigaset" brand to vigorously develop the digital cordless telephone business. In 2011, Siemens Phone officially changed its name to "Gigaset". So far, the "Gigaset" brand has sold more than 150 million digital cordless phones in 69 countries around the world, and is the world's leading brand in the field of telephones.

A cordless phone is a wireless duplex mobile phone device that can enter the PSTN. It consists of a landline connected to a PSTN subscriber line and one or more hand-held cordless telephones, which can perform the functions of an ordinary telephone within a limited range. The basis of the development of cordless telephones is the public local telephone network. At the time of the 1970s, PSTN was very popular in economically developed countries. Almost every household was equipped with ordinary electronic telephones. Telephones to solve problems in daily life and work have become people habit. However, the telephone set needs to be connected to the telephone office using a dual-core telephone line, and the landline of the telephone set must be connected to the handset equipped with a microphone headset using a four-core cable. Therefore, telephones are restricted and cannot be moved at will. For this reason, people connected an extension in other rooms to solve the problem of not being able to move at will. But if people want to make phone calls at outdoor activities, it becomes a big problem. Driven by this demand, a new type of mobile communication method has emerged. A cordless telephone set, such as a cordless telephone set, is connected between the handset equipped with a microphone and a headset and the telephone base.

Chinese name: cordless phone
Foreign name: Cordless telephone

Function: Call equipment
Appear time: year 1991

Product introduction

Cordless phone first phone

In 1991, Sanyo launched the "Te-Bu-Ra Cord Rusu", the first cordless telephone (with answering machine) in the telecommunications industry. ^[1]

Cordless phone

A cordless telephone is essentially an organic combination of a full-duplex radio station, a wired locale system, and a logic control circuit. It can realize a "cordless" connection between a slave and a landline through a radio wave medium in an effective field strength space. The most commonly used analogue cordless telephone. To put it simply, a cordless telephone is to separate the body and the handle of the telephone into two parts: the main unit (mother unit) and the auxiliary unit (sub unit). , Not limited by the traditional telephone handset cord.

How cordless phones work

The cordless telephone system can be divided into two directions: sending and receiving. Digital cordless phones are of course no exception.

CDCT (Chinese DigitalCordlessTelephone) uses multi-carrier TDMA / TDD format between landline and mobile phone. There are 10 carriers in total, each carrier has a bandwidth of 1.728MHz. Each carrier is divided into 24 slots in the time domain. A time slot can establish a duplex connection. When the call is established, the mobile phone only uses one-twelfth of the time to send and receive, and the remaining time can be used for other things, such as monitoring other frequencies and carriers to find a better voice channel.

Data signals and control logic signals of digital cordless phones are physically on the same carrier frequency. Therefore, before transmission of digital signals, time-domain compression is required. After receiving, perform time domain expansion.

cordless phone Considering the non-ideality of the wireless channel, the data must be channel-coded before transmission. In the design of the CDCT, error detection and post-error retransmission methods are used. Different channels use different redundancy coding. Two types of error detection coding are mainly used: R-CRC (16bitCRC) code and X-CRC (4bitCRC) code. The R-CRC code is mainly used in the channel coding of the A domain (control signal) and the B domain (data signal) which requires error detection and retransmission. The X-CRC code is mainly used for error detection coding in the B domain of non-error detection transmission.

Channel modulation mainly includes two aspects of multi-frame synthesis and code word scrambling. Code word scrambling is mainly to prevent the occurrence of consecutive 0 or consecutive 1 sequences. The modulation and demodulation of CDCT are implemented in the VCO open-loop state. Too many 0 or even 1 can easily cause the working point of the demodulator to shift. As a result, the bit error rate increases.

The frequency modulation adopts the modulation method of Gaussian minimum frequency shift keying. The modulation factor is 0.5. The nominal frequency offset is 288KHz. The digital signal sent from the baseband is directly sent to the modulation circuit after being filtered by a three-stage low-pass filter.

Cordless phone system implementation

In the system implementation, Siemens DECT baseband and RF IC are used.

The baseband IC includes PMB4925 and PMB4725. Among them, PMB4925 is a digital touch interface circuit. PMB4725 completes source coding, channel coding, encryption, and channel modulation. PMB4725 is a hybrid integrated circuit. It integrates MCU, DSP and BMC (BurstModeController). RF ICs include: PMB4420, PMB4220, and PMB4820. These three ICs and their peripheral circuits complete frequency modulation and demodulation.

New cordless phone The BMC completes the modulation and demodulation of various logical channels with strong underlying real-time performance; the DSP mainly completes the processing of data signals; the MUC is the control center of the entire system. It provides unified management of DSP, BMC and other peripherals. The power management module dynamically adjusts each part of the power consumption of the whole machine, so that the whole machine consumes the least power.

The call establishment process is as follows: When there is no call, the phone is locked on any idle channel. When a mobile phone initiates a call, it will send a call request in the corresponding time slot in the second half of the TDMA frame to notify the base station of the channel it has locked. After receiving the request, the landline notifies the mobile phone to go to the specified channel, and establishes a call on the specified channel. The process of making a call from a deskphone is similar.

The software protocol consists of five layers, from top to bottom:

Application layer (ApplicationLayerAPP),

Network layer (NetworkLayer-NTW),

Data Link Control Layer (DataLinkControlLayer-DLC),

Media Access Control Layer (MediaAccessControlLayer-MAC),

Physical layer (PhysicalLayer-PHY).

The control of the physical layer and some of the functions of the MAC layer are completed inside the control chip.

Resource management entity: The software process is based on a message-driven mechanism. The messages sent by each layer are scheduled by the resource management entity and sent to the target layer for processing. In addition, it is responsible for the allocation and management of memory and I / O resources; APP: implements the product Various functions and its user interface; NTW: responsible for call control and mobility management; DLC: responsible for two-way data transmission between landline and mobile phone, providing error control; MAC: selecting and dynamically assigning physical channels; low-level device drivers : Including control of LCD, keyboard, EEPROM, DSP, etc.

New standard for cordless phones

In order to meet the market's demand for digital cordless telephones, and to consider the spectrum requirements of China's third-generation mobile communication systems in the future and to effectively use limited radio spectrum resources, the Radio Administration Bureau of the Ministry of Information Industry has made a temporary use of frequency bands for digital cordless telephones. New regulations. Digital cordless phones using the frequency band between 1915 and 1920MHz will be ordered to stop production in China after two years.

Creative cordless phone The specific contents of the new regulations include: Digital cordless telephones are managed as micro-power (short-range) radio equipment. For specific regulations, please refer to the "Interim Regulations on Micro-power (Short-range) Radio Equipment" of the Ministry of Information Industry (Xinbu (1998) No. 178) . Its technical indicators are tentatively set to temporary use frequency: 1915-1920MHz; transmit power, average power transmitted by landline and mobile phone 8mW; peak power 250mW; stray emission power level limit: stray emission power relative to carrier level ( Attenuation) 50dB, or absolute level 2.5W; frequency tolerance 20ppm.

The above-mentioned frequency is temporarily used until December 31, 2002. From January 1, 2003, production and import of digital cordless telephones in the above frequency bands will be stopped, and used telephones can be used until they are scrapped. In the future, the Radio Management Bureau of the Ministry of Information Industry will consider the long-term use frequency of digital cordless telephones according to the corresponding technological developments at home and abroad.

Cordless phone radiation

Cordless phones have become the first choice for more and more families to purchase telephones because they are not bound by a telephone line, which is convenient and practical. The cordless telephone connects the handset and the handset by means of radio transmission and reception, so that the handset can also talk. Many consumers are worried about the use of cordless phones after suffering from the electromagnetic wave radiation of mobile phones, and some consumers are still attaching a sheet to eliminate electromagnetic waves on the receiver. How much radiation does a cordless phone have? Does the electromagnetic wave emitted by the cordless phone affect the human body?

Ear cordless phone It is understood that the Radio Regulatory Commission clearly stipulates that the transmit power of cordless telephone landlines and handsets must not exceed 20 mW, and the open talk distance is about 300 meters, and the low-frequency frequency between 45 and 48 megabytes is selected. This transmit power is at low frequencies. The radiation generated within the range is very small and will not cause any impact on the human body.

It may be useful to compare the parameters of mobile phones used by everyone with cordless phones. Most of the transmitting power of mobile phones is 2 watts and the frequency is 900 megabytes. The transmitting power of mobile phones is 100 times that of cordless phones, and high-frequency transmission is used. There is no definite scientific basis for whether mobile phones will have adverse effects on the human body, and the use of microwave radiation generated by low-power transmission of cordless phones will not cause any impact on the human body, which can be almost ignored, and consumers need not worry.

Cordless phone product advantages

Regarding the development of digital cordless telephones, the Ministry of Information Industry had already prepared for the situation two years ago and introduced the 2.4G digital cordless standard to regulate the digital cordless telephone technology market. The release of frequency bands has cleared the way for the introduction of digital cordless phones. But at the time, digital cordless was more of a technical concept that was not well known to the public. So what are the advantages of digital cordless technology?

Digital cordless telephones have six major advantages: high-definition call sound quality, security, confidentiality and anti-interference, a larger call range, low power consumption and long-lasting power, expandable internal calls, and health and environmental protection with low radiation. Compared with the 45- to 48-megabit analog cordless phones, 2.4G digital cordless phones have obvious advantages in terms of communication distance, sound quality, anti-interference, and confidentiality. This is exactly the most direct reason for digital upgrade of analog cordless phones. . The specific advantage is that the sound quality is clearer than analog cordless phones; moreover, due to the use of digital communication technology, the communication distance can be very long. Using digital cordless phones can be up to 300 meters away from the main unit in a spacious environment without radio interference. Meanwhile, first

Streamlined cordless phone The advanced digital technology has very good confidentiality and anti-interference, which means that the phenomenon that "you can eavesdrop on a cordless telephone conversation with an ordinary FM radio" no longer exists.

Although digital cordless has unparalleled technical advantages, due to the high price of early digital cordless phones, which exceeded the affordability of most domestic households, its users in China were only a small number of high-end users during the early promotion. Although Siemens has been vigorously promoting the concept of digital cordless, but due to the size of the industry, the price of digital cordless has always remained at a high level. Many consumers are full of expectations for digital cordless, but there is no purchase due to price restrictions.

Now the Chinese economy continues to improve, the housing market continues to heat up, and the living of Chinese people has improved qualitatively. Therefore, the traditional analog cordless technology can no longer meet the high-quality communication needs of families.

Siemens (China) Co., Ltd. officially released its latest digital cordless phone C42 in China. As soon as it debuted, it became the focus of the market with a high cost performance of 500 yuan. Previously, the price of domestic digital cordless phones was generally between 700 and 1600 yuan. The debut of C42 will break the ice of the digital cordless market and sound the horn of China's cordless phones entering the digital age.

Cordless phone growth momentum

Due to the good development momentum of the digital cordless market, Putian, Capital, DBTEL, Tsinghua Tongfang, TCL, China Hi-Tech and other brands have also begun to test the water and continue to increase follow-up efforts. Phone manufacturers such as Siemens, Woori and Capital have already obtained 2.4GHz phone network access licenses from relevant national authorities, while more manufacturers are waiting for licenses. In fact, after the 2.4GHz frequency band was opened to the communications industry two years ago, companies continued to enter the 2.4G digital cordless phone market, but the price was too high at the time and the market could not afford it.

Based on such a bright future, there are already many brands in this market, and many models are waiting for network access licenses from the Ministry of Information Industry. It is not difficult to conclude from this that after two years of hard work, digital cordless has reached a market tipping point, and 2005 has become a veritable digital cordless year.

cordless phone

Demand for cordless phones

Relevant market research shows that there are about 15 million to 18 million cordless phones in use in China. The sales of cordless phones account for about 5% -6% of the sales of fixed telephones, while the penetration rate of cordless phones in developed western countries is as high as 45% or more. China is expected to shorten or even close the gap rapidly in the next five years. The market potential is undoubtedly huge. Digital cordless sales only account for about 6% of cordless phone sales, but the popularity of digital cordless is already the general trend. It is expected that the number of analog rotations will be basically completed in the next three years. Many Chinese consumers will also enter the digital cordless era directly from corded phones.

Market veterans believe that after several price adjustments and technology maturity, and the general improvement of urban residents' living standards, the application of digital cordless phones will soon become a home consumer fashion, and this market is expected to enter a rapid growth period.