Data processing: speech signal processing – linguistics – language – Speech signal processing – Application
Reexamination Certificate
2000-08-15
2003-05-27
McFadden, Susan (Department: 2654)
Data processing: speech signal processing, linguistics, language
Speech signal processing
Application
C704S270000, C455S439000
Reexamination Certificate
active
06571212
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to communication systems and protocols for voice communications and, more particularly, to a communication system and protocol for transmitting and receiving voice calls over the Internet where at least one terminal is a mobile terminal.
Mobile wireless communications have evolved into a well-established field with numerous industry standards for both analog and digital communication systems. In digital wireless communication systems, undue degradation to the voice quality can be substantially prevented even though the digital data suffers from uncorrected transmission errors. For example, in British Patent No. 8,119,215 to Applicant, a method of detecting errors in frequency-hopping transmissions of digital voice data is described, wherein the data from hops determined to be in error is replaced by data deemed not to be in error. The new data preferably corresponds to the voice signal one or more whole pitch periods earlier or later in time. Since the introduction of this technology, digital mobile communication systems have employed bad-data replacement to maintain the highest possible voice quality under marginal radio conditions. Such methods are variously known as “deburping,” or more scientifically, as “artificial parameter reconstruction” (APR). The detection of uncorrected errors and their handling by APR typically occurs immediately upon reception. Moreover, the compressed digital voice formats used for wireless transmission are generally converted to standard Pulse Coded Modulation (PCM) or analog voice waveforms for further transmission over the telephone network.
In prior art digital mobile communication systems, it is also known to use digital encryption over the wireless communication link, which is otherwise too easily intercepted. A user specific encryption key is typically established for each call at the mobile terminal and at the base station serving as the present host for the mobile terminal. The encrypted data transmitted from the mobile terminal is then deciphered at the base station so that it is possible to manipulate the plain text voice bits in the APR algorithm. After deciphering, the base station may pass the call to the Public Switched Telephone Network (PSTN) so that the intended recipient may receive the call. The transmission over the PSTN or other wire-based network is generally unencrypted. Consequently, communications remain vulnerable to interception on the PSTN or other wire-based network. In theory, such interception is only legally possible by law enforcement agencies, but there are no safeguards against illegal interception. Thus, sensitive information may actually be better protected during a wireless transmission than a wire-based transmission.
With increasing amounts of sensitive financial, personal, technical, and business information being transmitted over the Internet, there will be increased concern for security and greater use of encryption. Imminent changes to government policy are likely to sacrifice access by law enforcement agencies to wire-based networks for the greater benefits of security in general, thus encouraging more encryption on wire-based networks. An initiative promoting this attitude is known as Safety and Freedom through Encryption, or SAFE for short. However, to date, there has been no real effort to provide mass encryption of communications over wire-based networks.
Another recent development is the use of the Internet for voice calls, known in the industry as “IP voice.” Since Internet access is essentially a subscription-charge-only service, with no usage charge for minutes or long distance, this arrangement is attractive to subscribers. To date, IP voice has only been used for calls between fixed subscribers, i.e., those connected to wire-based networks.
Mobile subscribers can be connected to fixed subscribers using IP voice. However, the protocol over the wireless communication link is normally the standard circuit-switched wireless protocol. Conversion to Internet Protocol (IP) is done at a wireless network station, such as a base station. In the future, mobile communication systems known as third generation mobile communication systems will allow the Internet Protocol (IP) to be extended over the wireless link. For example, GSM's General Packet Radio Service (GPRS) and a development thereof known as EDGE, are currently being planned and implemented. IP is an end-to-end protocol. The transport mechanism is, in principle, a bit-exact transport mechanism, meaning that the protocol ensures that all bits are transmitted correctly. If encryption is used, it is end-to-end encryption. It will be appreciated that, if traffic is end-to-end encrypted, it is impossible for the wire-based network to determine whether a given quantity of bits represents speech or computer data, and therefore, it is impossible to have differential pricing. Likewise, it may be difficult to perform APR in the mobile communication network, which requires modification of plain text data.
To date, IP voice is in an embryonic stage of development that has been conceived for calls between fixed terminals, without taking into account the specific needs of wireless communications and the implication of bit-exact protocols or end-to-end encryption. Thus, there is a need for an IP voice protocol that accommodates wireless communication and end-to-end encryption and that is compatible with existing mobile communication technologies.
BRIEF SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of prior art IP voice networks by accommodating the needs for wireless communications while still allowing end-to-end encryption. According to the present invention, when a digital speech signal is formatted for transmission over a wireless communication link, a blank field, referred to herein as an error indication field, is appended to each speech data packet. The bits of the error indication field are initially set to a value indicative of no error. The speech bits and error indication bits in the speech data packet are then separately encrypted, for example, by bit-wise encryption. Error correction and error detection coding are performed following encryption. By performing error coding after encryption, it is possible to detect errors at the receiving end without first decrypting the message. Also, the use of bit-wise encryption allows bits in the error indication field to be inverted to give an error indication without decrypting the message. Thus, the present invention allows the error indication to be added to an already-encrypted message without altering the total number of bits contained in the message. The ability to add an error indication to an already-encrypted message without changing the total number of bits allows use of end-to-end encryption and other end-to-end protocols, such as the Internet Protocol (IP), without causing protocol stack violations.
In one embodiment, a system for transmitting speech from a fixed terminal to a mobile terminal is disclosed. Analog speech is received at a fixed terminal, converted to a digital signal, and then turned into speech bits by a vocoder. The speech bits are transmitted in a speech frame having an error indication field. The bits of the error indication field are initially set to a default value indicative of no error. The speech bits and error indication bits are encrypted, preferably with bitwise encryption technology, to generate an encrypted speech signal. The encrypted speech signal is then formatted for transmission over the Internet to a wireless base station. The wireless base station strips the Internet formatting from the message and performs error detection coding and error correction coding on the encrypted speech signal. Then, the base station formats a message for transmission over the wireless communication link to the mobile terminal. The mobile terminal receives and demodulates the message, and then performs error correction and detection decoding on the still-encrypted signal. An error indication is
Coats & Bennett P.L.L.C.
Ericsson Inc.
McFadden Susan
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