Fixed Wireless Broadband is better than Mobile.

Most research and papers on Mobile Data consider Mobile use, not indoors at home or an office. This article compares Mobile and Fixed Wireless for provision of Data / Internet in a Fixed location.

The Mobile systems use an indoor aerial that is Omni-directional and typically -2dB gain. Indoor has -6dB to -20dB path loss penalty compared with a Roof mounted aerial. In addition, depending on frequency and aerial size, the roof mounter or outdoor aerial for Fixed Wireless has a beam-width from 45 degrees down to 1 degree and is a known fixed polarisation. A Mobile / Nomadic system generally has to use co-polar diversity transmission and reception on +45° and -45° but a Fixed wireless system can use different polarisation (plane or circular) for each sector or cell.

There is a maximum performance of speed for any given spectrum for a given Power or SNR (Signal to Noise).
There is a low limit to power on the indoor Mobile modem transmitter due to:

• Avoiding inter cell interference, reusing frequency (channels, spectrum)
• Regulator limits
• Possible Safety concerns (burns or corneal damage at high power rather than Cancer)
• Mobile typically limited by 5V @ 500mA USB (2.5W total)
• Low PA efficiency to allow QAM operation.
• Battery operation (Mobile primarily designed for phones)

The limit of of speed versus SNR is independent of technology and set by basic mathematics as shown by Shannon and Hartley. All Modern system get close to the theoretical limit.

(EVDO is the USA Mobile data system based on CDMA-1, 802.16 is WiMax, HSDPA is variable QAM data only on 3G phone network)
To relate that graph to actual speeds we need to know the power, path length and bandwidth. HSPA uses 5MHz. The Absolute distance is not important. At cell edge we pick the level of power where real SNR and and Intercell interference give about -12dB SNR.

On CDMA systems using more hopping codes reduces range, but increases capacity as each looks like noise to the others. Thus the greatest range is if only one code is in use. The range is a lot less if all 15 codes are used. This is why WiMax and LTE don't use CDMA. 3G/HSDPA is CDMA based so range breathes with number of users.

Relationship of Modulation, FEC and Hopping codes

Newer systems can use higher QAM, but only if signal is good.

If we assume people are EVENLY distributed in a Sector, (which isn't true, the reality is more complex) then simplfing possible speeds and number of people per area as a constant gives:

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Distribution of users vs available speed for single user connecting.

You can see that increasing speed from 3.6Mbps -> 7.2Mbps -> 14.4Mbps -21Mbps makes ZERO difference to most people. The higher speeds is just a software change to have increased QAM. It does nothing for range (Shannon) and can only apply to an ever smaller area (Shannon).

You can see why it's hard to get more than 2Mbps. You can also see why if ten people are connected simultaneously downloading the speeds per user vary from 50kbps to 250kbps depending where you are in the sector. It's nearly impossible to have average throughput for all users together above 2Mbps unless everyone is much closer to to mast than cell edge.

Providing the user Modem has not reached full power the actual cell size is irrelevant as in a city with small cells the Modem and base power must be scaled back to same SNR as a larger rural cell to avoid inter-cell interference.

Here is % Users (evenly distributed by area) versus speed for various HSDPA or iHSPA downlink speeds on Log Log scale so you can see the sub Mbps speeds and sub 1% user numbers.

Peak Speed for one user versus Location

This shows clearly that a well engineered Fixed Wireless system gives everyone the Peak "close to mast" performance of Mobile. Less than 2.5% of users see any speed increase difference for a 3.6Mbps HSDPA and 21Mbps iHSPA system on downlink. Less than 25% of Mobile System users (indoors in fixed usage) will see a peak speed more than 500kbps, even if only one user is connected.

For over 97% of Mobile users, if users are evenly distributed in a Cell, the peak 3G speed from 3.6Mbps to 21Mbps makes no difference. This has little to do with Radio System (Technology) but Fixed Roof Directional aerial versus indoor omni-directional Mobile aerial. You can substitute 5MHz Mobile WiMax or 5MHz Mobile LTE and the brown 21Mbps iHSPA downlink line for one user versus location will be unchanged. You can use almost any 64QAM Fixed Wireless system with parameters for Roof Mounted Directional Aerials and you will get the flat green line of 21Mbps @ 5MHz channel for all users, with one user connected.

With a Fixed wireless system engineered for better than 20dB SNR, everyone gets 21Mbps 64QAM speed. With a minimal 6dBi aerial on roof you will see an improvement of 14dB to 28dB SNR even at the same Modem and Base Station power as the indoor loss is 6dB to 20dB compared to roof and the Mobile Modem Aerial is typically -2dBi gain. Small low cost commercial patch antenna 10.5GHz systems have at least 18dBi and a basic flat panel 900MHz roof aerial is 7dBi gain.

An HSPA user Modem is typically 300mW maximum, at 400MHz to 870MHz regulators typically allow up to 1200mW) which is 6dB more, giving a minimum link budget upgrade of -2dB -> +7dB = 9dB for aerial, 6dB to 20dB for Location and +6dB for power giving a total of 9 + 6 + 6 = 21dB extra on SNR. At -3dB to 0dB SNR the speed of HSPA is about 1Mbps to 2Mbps. For the Fixed Wireless system on 400MHz to 900MHz, with a minimal roof aerial we have 21Mbps, with no extra intercell interference. At twice the distance you can use an aerial with 6dB more gain. At 800MHz this would be a Yagi and at 3.5Ghz a modest flat panel (A typical MMDS aerial at 2.5GHz has 22dB gain).

Next we will look at base Sector versus Mobile Modem polar pattern and what a Fixed Wireless system does. Both systems plotted to same receiver sensitivity, the edge of red is about -80dBmV.

(The raggedness is an artefact due to low terrain file resolution)

The directional aerial on fixed systems assures that neighbouring cells do not have interference despite greater power that allows 64QAM at greater range than Mobile lowest QPSK speed of cell edge.