Unconditional Secret Code Secret Wireless Communications System Design

The rapid development of wireless communication facilitates human-being's daily life, and the signal transmitted has transformed from voice to full service which include voice and data. Transmission bandwidth and rate has been improved gradually as a result of growing demands. Meanwhile, security of wireless communication system is facing a new challenge.In traditional security communication system, the method of using encryption key to encipher data in application layer was adopted. However, this technology can not implement perfect secrecy because of the rapid development of computer industry. A secure key chosen to encipher data recently may be not secured in a few years. On the other hand, using this encryption technology need a perfect confidential channel for key distribution, management and destruction. In case this channel can be access arbitrarily, our communication system is not secured any more.Different from traditional security communication system, physical-layer security techniques whice using all aspects of physical-layer transmission technologies just like modulation, coding to replace data encrption were adopted in this paper. Noise of channels is very important in this method, the target is clear that hiding messages in noise that eavesdropper can not decode the messages.It is known that in wiretap channel I model, the eavesdropper is assumed to receive messages transmitted by the sender over the channel that is noisier than the legitimate receiver's channel. Under this condition, it is possible to establish a perfectly secure source-destination link without relying on a shared secret key. However, how can we establish wiretap channel I and which coding can we chose to implement unconditional security communication have not been shown.In this paper, we study the method of using secure coding to implement unconditional security communication system firstly, and propose that a class of linear codes called optimal error detection codes can be using. After simulation of these codes in our system, we found it is achievable to implement security communication system. The codes involved in this paper were BCH codes, Hamming codes, Golay codes and first-order RM codes. We can conclude from the simulation that for any input information exceeding the threshold error rate at different coding rates, secure coding has the ability of"error exoansion". Therefore, when the error rate of main channel is less than the threshold, the legal receiver can decoding the messages, on the other hand, when the error rate of wiretap channel is more than the threshold, the illegal receiver cannot decoding the messages.Secure coding of unconditional security communication system is at a starting stage, there are lots of works to do in the future.