One way to increase spectral efficiency is to add the number of diversity paths both at transmits and receiver ends. In 1997, Siavash Alamouti and Vahid Tarokh introduced the transmitter diversity and shown Space Time Code, aka STC, enhances the signal quality at the receiver. Alamouti also suggested that the technique can be extrapolated to multiple transmit and multiple receiver path, what has become to be Multiple Input Multiple Output, aka MIMO. MIMO has already been used in 802.11ac and 802.11ad WLAN Technologies. 5G Technology will rely on massive MIMO to achieve 10Gbps data rates and higher. Currently, Alamouti and Tarokh are Mimik CEO and Area Dean for Electrical Engineering at Harvard University, respectively.
Theodore (Ted) S. Rappaport (November 26, 1960 – present)
Radio/wireless communications in metropolitan area faces multipath fading phenomena. Drive underneath a bridge in highway while listening/tuning to an AM radio channel; and you will experience multipath fading first hand. In 1987, Rappaport cataloged and formulated various multipath fading channel manifestations, which are used today to characterize any fading environment. Therefore, system designers can mitigate it with designing modulation scheme, equalizer, receiver diversity, and error correction coding. Rappaport’s contribution to 5G technology will be instrumental to achieve high data rate and/or throughput. Currently, Rappaport is the David Lee/Ernst Weber Professor of Electrical and Computer Engineering at New York University.
Robert W. Chang
In order to mitigate multipath fading of the desired signal in metropolitan area, Orthogonal Frequency Division Multiplexing, aka OFDM, is utilized. In 1966, Chang introduced OFDM at Bell Labs. OFDM increased spectral efficiency, lower multipath fading, and immunity to narrow band RF interference. It also reduces the complexity of receiver equalizer significantly. OFDM technique has played key role in ADSL, WLAN, DVB-T, UWB, DAB, SDARS, and ISDB standards so far, and will be likely to be evolve into Filter Bank Multi Carrier, aka FBMC, or Orthogonal Time Frequency Space, aka OTFS, for 5G technology.
Andrew Viterbi (March 9, 1935 – present)
One of the advantages of digital over analog communication is the ability to include additional coding to the original signals/messages in the transmitter and leverage the codes to decipher correctly the received signal/message over the noisy channel. Over the last couple of decades, many coding algorithms are developed and used in digital communications industry. Invented in 1967, the Viterbi algorithm is known to be a dynamic algorithm which can detect the most likely sequence of digital states among all possible combinations. Therefore it is widely used in many applications, such as, Satellite, Mobile, WLAN, and 5G technologies. Andrew Viterbi is currently the Presidential Chair Professor of Electrical Engineering department at University of Southern California.
Jack Wolf (March 14, 1935 – May 12, 2011)
Although coding is an advantage from reducing the number of errors over noisy channel aspect, it requires additional spectrum and power to deliver the intended message. The spectrum and power overhead is directly proportional to the number of coding bits required to be added to the original message. Wolf’s contribution to digital communication was subtle, yet very important to the efficiency of signal transmission, decoding, and storage. Wolf’s technique becomes particularly important to 5G where efficiency of digital signal delivery will be prime important in order to achieve high data rate with less power. Jack Wolf was professor of Electrical Engineering at University of California, San Diego.
Claude E. Shannon (April 30, 1916 – February 24, 2001)
In digital communication, there is fundamental question of the limiting factor in transmitting and receiving appropriately any data over noisy channel. In 1940, Shannon developed Channel Capacity theorem which formulate the relationship between channel capacity, bandwidth and signal to noise ratio. Since then, this theorem is used as a metric and upper bound for spectral efficiency of any wireless communication systems. The theorem is referred to as Shannon Channel Capacity theorem.
Harry Nyquist (February 7, 1889 – April 4, 1976)
Information to be transmitted and received in any wireless communication systems is analog, in nature. In converting any analog information to its digital representative, the fundamental question is, how fast an analog signal has to be sampled such that the original information is not lost and/or distorted after reconstruction at the receive end. In 1928, Nyquist developed a theorem which is widely used in the industry to determine that sampling rate of any desired signal based on its bandwidth content. The theorem is referred to as Nyquist Theorem and the sampling rate is known as Nyquist rate.
Edwin Howard Armstrong (December 18, 1890 – January 31, 1954)
Since Hertz’s experiment, the radios designed were Tuned Amplifier architecture, TA. Tuned Architecture radio design consisted of series of amplifiers and tuned filters which has very limited dynamic range, and hard to manufacture, therefore limited applications, high maintenance, bulky, and expensive.
Armstrong working on TA various radio, noticed that near some radio stations, there could be mixing/beating of two different frequencies and creating upper and lower band of the same signal. He realize that the mixing of these frequencies has to be due Heterodyne phenomena, (Hetero antonym to Homo, two different frequencies in this case, whereas Dyne means mixing).
In 1918, Armstrong invented Super Heterodyne, aka Superhet, architecture which consisted of RF and IF signal conversions. Superhet has wide dynamic range which translates to very low receiver sensitivity, the most critical parameter of any receiver. This architecture consisted of LNA, RF frequency conversion/mixer, Image rejection filter, IF frequency conversion/mixer and channel select or Anti-Aliasing filter. Superhet architecture was the only architecture in any industry until 1990’s. To this day, this architecture wins when high performance radio is needed.
Heinrich Rudolf Hertz (February 22, 1857 – January 1, 1894)
In 1887, Hertz was the first engineer who designed an experiment to put Maxwell mathematical formulations and observations to test. Hertz successfully designed the 1st 50MHz Dipole Transmitter and Loop Receiver Antennas to transmit and receive electrical signal across his laboratory. He was able to validate Maxwell predication of electromagnetic waves at the speed of light. This was beginning of wireless communications as we know it today. Hertz’s experimental apparatus was the 1st radio for wireless communication. This is perhaps the reason why today his name still is alive/known in radio communications as the unit of frequency and bandwidth by any electrical engineer.
James Clark Maxwell (June 13, 1831 – November 5, 1879)
Magnetic property and electric current was well known prior to Maxwell discoveries. In fact, it was Faraday and Ampere who designed experiments to demonstrate and quantified the relationship of Static magnetic and electric fields. In both these discoveries, the electric and magnetic fields were Statics, i.e. location varying fields. In 1865, Maxwell published a paper that demonstrates his realization that constant current generates location varying magnetic field, thus no varying electric field. More importantly, he realized the missing puzzle; namely, time varying current, i.e. electrons accelerated or decelerated electrons, causes location and time varying magnetic field, which in turn generates location and time varying electric field. As a result of location and time varying ElectroMagnetic fields, electromagnetic wave propagates with speed of light, even after the source/current is removed. Although Maxwell’s mathematical discoveries were on papers, they shifted the minds of many scientists, engineers (e.g. Hertz), and entrepreneurs (e.g. Marconi) soon after him to entertain wireless communications.