6G: OFDM (Orthogonal Frequency Division Multiplexing)

6 G is expected for 2025/30, there are several ideas for the next generation, although it looks that OFDM is here to stay.

Trend 1: More spectrum, more bits: The challenge of achieving tens of Gb/s, at least in an aggregated sense to a small region, will depend on finding yet more spectrum There are several bands between100 and 300GHz that show some promise.

Trend 2: Increased Emphasis on Spatial Bandwidth: There are some efforts to enhance massive MIMO beyond the current state of the art with 6G as their target.

Trend 3: New Technologies: Antenna technology is seeing a lot of activity right now and there is a strong expectation that antennas in the mmW and above will be embedded on chip in handsets and then later in small cell solutions.

Trend 4: New Applications Support: The first standard of cellular designed primarily for machine to machine communication and this will have a dramatic impact on the requirements for QoS and roaming. Other general application classes include the Tactile Internet, the Internet of Skills and Autonomous Vehicles.

Trend 5: 5G fixes: 5G is implementing many fundamental changes, some of them will have to be fixed.

5G: OFDM (Orthogonal Frequency Division Multiplexing)

5G deployment started in 2019 and full deployment should happen in 2021. The new architecture has the following evolved features:

  • A new core, denominated 5GC and divided in the following functionalities
    • Authentication and Mobility Functions (AMF)
    • User Plane Functions (UPF)
    • Session Management Functions (SMF)
  • A new radio denominated NR (New Radio), which has multiple subcarrier numerologies (multiple subcarrier spacings) and is used in two types of Bases Stations:
    • ng-eNB: 4G eNB (Base Station) that supports connectivity with 5G radios
    • gNB: 5G Base Station

This 5G version of LTE was partially specified in Release 15 (2018) and completed in Release 16 (2020), when it should become the ITU (International Telecommunications Union) IMT-2020 (International Mobile Telecommunications).

The NR leveraged the OFDM flexibility and allowed several spacing configurations. The frame format was made more flexible, but too many options had to be included to satisfy all the parties. Finally, some anachronisms of the original specifications were practically abandoned as extended cyclic prefix and DFT-S-OFDM.

The main issue was not addressed though. The channel diversity specified in WIMAX (permutation) was not adopted, so the channel diversity continues poor.

The use of high frequencies and small cells will not be the panacea advertised but will address some situations (not many). Small cells can be used in 4G, as well as the high frequency bands.

In conclusion, 5G is a slightly enhanced 4G. The marketing promises by 3GPP are huge, but the reality is much more modest.

4G: OFDM (Orthogonal Frequency Division Multiplexing)

The OFDM technology was developed by R.W. Chang from Bell Labs in 1966, but its practical implementation was not feasible at the time.

In 1999 IEEE specified OFDM for its 802.11 wireless local network as 802.11a-1999 (5 GHz initially and next 2.4 GHz), with the commercial name as Wi-Fi (Wireless-Fidelity). Soon this solution took over the world and it is the most pervasive wireless implementation, present in most homes and commercial establishments.

In 2001, IEEE issued 802.16, commercially denominated as WiMAX (Worldwide Interoperability for Microwave Access). It became the first OFDM carrier 4G system to be deployed.

3GPP released its own OFDM version in 2009 (Release 8), under the commercial name of LTE (Long Term Evolution). LTE benefited from the WiMAX field experience and was supported by the European Community and its vendors. It was constantly updated through additional releases (Release 9- December 2009, Release 10- March 2011 (LTE Advanced), Release 11- September 2012, Release 12- June 2014, Release 13- December 2015 and Release 14- June 2017).

The demand of wireless communications continues to grow, and operators are running out of spectrum capacity. New applications, like IoT and M2M, are popping out and they require new capabilities, not required before. This open the doors to private networks powered by specialized vendors.

Operators and traditional vendors realized that their implementation (4G LTE) could not cope neither with all the requirements, nor the demand. Besides it had some inherited flaws since its inception.

A new architecture and a new radio were required to further evolve the technology. This evolution was labeled by 3GPP as 5G, although technologically it is still the same OFDM as 4G.

3G: CDMA (Code-Division Multiple Access)

This technology was developed by Qualcomm and adopted by TIA in 1995 as IS-95, under the commercial name of cdmaOne and later cdma2000. Data capability was added with EV-DO (Evolution Data Only) in 1999, RevA/B in 2006 and SVDO (Simultaneous Voice and EVDO) in 2011.

The Europeans developed their own standard under the name of UMTS (Universal Mobile Telecommunication Standard). The first specifications were done by 3GPP in release 99 (1999). Data capability was added with HSDPA (High Speed Downlink Packet Access) in 2005, HSUPA (High Speed Uplink Packet Access) in 2007 and HSPA+ (High Speed Packet Access) in 2009.

2G: Digital (TDMA)

The analog signals used in 1 G were digitized with the intention of increasing capacity. The first digital implementation was specified by TIA as IS-54 and later IS-136. The IS-54 standard was published in 1990 with the marketing name of D-AMPS. It multiplexed 3 digital channels into 1 AMPS channel. The first commercial network was deployed in 1993. The European Countries issued their own digital implementation GSM (Groupe Spécial Mobile, alter renamed Global System for Mobile) in 1991. Data capability was added with GPRS (General Packet Radio Service) in 2000 and EDGE (Enhanced Data Rates for GSM Evolution) in 2003.

1G: Analog

This technology established the concept of cells, that allowed the wireless boom. It was conceived by Bell Labs and published in the Bell System Technical Journal (Manuscript received on August 1, 1978, by N. Ehrlich, R.E. Fisher and T.K. Wingard and published in BSTJ vol58, No1, January 1979). The marketing name was AMPS (Advanced Mobile Phone Service) and it was first implemented in 1983. European derivatives were called NMT (Nordic Mobile Telephone) and TACS (Total Access Communication System).

The first implementation used 30 kHz channels in the 800 MHz band.