TM-UWB Technology and Its Application in wireless communication)

Traditional communication systems are usually fixed-frequency communication systems. The information to be transmitted uses a fixed bandwidth, and the signal is modulated to a fixed frequency band and then transmitted over a channel (wireless or wired. Any other signal in this channel will interfere with useful signals. Therefore, a communication system with such characteristics is called a fixed-frequency communication system with an exclusive Channel. In contrast, the wireless signals sent by Ultra-broadband (Ultra-Wideband) wireless communication systems or transient pulse radio systems do not occupy a fixed bandwidth, it spans a wide range of wireless spectrum (generally in 1 ~ 10 GHz), and the power is very low, similar to the background "noise", so it will not interfere with other wireless signals working at the same frequency.

The ultra-wideband Communication System has many outstanding performance characteristics, that is, the signal power spectral density is extremely low. The transmit power consumption of the ultra-wideband system is much lower than that of the traditional radio technology, you can use an average power less than 1 MW to cover a few miles, or even use a low-gain antenna. It is particularly valuable that it has low Interference Characteristics and strong multi-path interference resistance to other wireless systems. It is easier to implement than to build a common spread spectrum system, with a low cost. It is precisely because of the above features that the UWB communication technology has been widely used in personal communication, intra-building communication, high-speed LAN, cordless phones, security systems, close-range and high-precision positioning, and other aspects.

TM-UWB Technology and Its Characteristics

TM-UWB Signal

In general communication systems, "broadband signals" refer to signals with large modulation bandwidth and high data transmission rate. The Ultra-Wideband Signal refers to the signal's Fractional bandwidth (Fractional Bandwidths, FBW) (the ratio of the signal bandwidth B to the center frequency f c, that is, B/f c) is greater than 0. 25 or 25%, which is usually directly modulated by an impulse pulse with steep rise and fall times to obtain a modulation signal with a gigabit Hz (GHz) bandwidth, it is also called "baseband signal" or "no carrier signal ". Its bandwidth is very wide, and the spectrum is often extended from DC to GHz. This signal is widely used because of its advantages such as high resolution, high processing gain, low theft, large information content, and ability to detect hidden targets.

TM-UWB communication system is a brand new communication system, which can transmit data, voice and even images with low power and similar noise in transmission media. Because TM-UWB technology is used to transmit wireless signals across a wide range of wireless spectrum, and the power spectrum density is very low, similar to the background "noise, therefore, it will not interfere with other wireless devices working in the same frequency band.

Selection of transmission Waveforms

Generally speaking, the Communication System Using TM-UWB technology is not a sine wave signal, but a pulse interval strictly controlled Gaussian single week ultra short pulse, the general working pulse width is 0. 2 ~ 1. 5ns, recurrence: 25 ~ 1 000ns. The ultra-short Cycle Pulse determines the wide bandwidth of the signal. This system uses time (Pulse Position) modulation to carry information and perform channel coding. The receiver of the TM-UWB communication system directly converts the received RF signal into a base band digital or analog output signal. the electromagnetic pulse sequence can be converted into a base band signal by using only the first-level front-end cross-correlation device, without the intermediate frequency level in traditional communication devices, the complexity of communication system devices is greatly reduced. A bit of information is usually extended to more than one ultra-short pulse in a single week, and the receiver integrates the appropriate number of pulses to restore the sent information.

Gaussian pulse with Ultra Short Cycle

The most basic and important task in TM-UWB RF technology is to obtain the Gaussian single week pulse in practical application. Figure 1 shows the time-domain waveform and frequency-domain characteristic curve of a typical Gaussian ultra-short cycle pulse (with a center frequency of 2 GHz.

The time-domain and frequency-domain mathematical models of Gaussian single-week pulse can be expressed

In formula, A is the pulse peak amplitude, and Tau is A time delay length, which is equal to the pulse duration, t is the time, f is the frequency, the center frequency f 0 = 1/Tau can be introduced, and the half-power bandwidth Wb = f 0 x 116% can be used to obtain the pulse width of 0. 5 ns Gaussian single week pulse, the center frequency is 2 GHz, half power bandwidth is about 2 GHz.

Single week Pulse Sequence

The TM-UWB system uses a long sequence of single week pulse in actual communication, rather than a single week pulse. Data modulation and channel coding are implemented by changing the time interval of the pulse sequence. Figure 2 shows the time domain and frequency domain features of a single week pulse string. Due to the recurrence of Time-domain signal rules, the frequency spectrum is discretization, resulting in strong energy spikes. These peaks will interfere with traditional wireless communication devices and signals, this is not expected to happen.

Because a well-regulated time-domain pulse sequence will not carry any useful information, changing the time-domain pulse sequence rules can also reduce the energy spikes in the spectrum, therefore, the Time Modulation (TM) technique or Pulse Position Modulation (PPM) technique is often used in information Modulation and channel encoding.