September 19, 2012

The iPhone 5 and radios for cellular and WiFi

The cellular radio side of the iPhone 5 has access to superfast (up to 20 megabits per second) networking via LTE 4G broadband, keeping up with the iPad and some of its competitors.  This is the first time that the iPhone truly supports 4G. Yes, I know that iPhone 4S on AT&T showed “4G” but it was really just 3G (although AT&T’s 3G is faster than Verizon’s). Unlike the iPhone 4S which was a “world phone” meaning one model works for all carriers with dual GSM/CDMA support, the LTE-enabled iPhone 5 comes in two separate GSM models and one CDMA model. This means that consumers will have fewer choices when switching carriers, and that LTE access will be limited when traveling abroad, depending on the model you have. Although the “CDMA” model (for Verizon and Sprint) is more universal  than the “GSM” model for AT&T – it supports CDMA, EV-DO, GSM, UMTS and 5 LTE bands and is likely a better world phone.

On the WiFi radio side it is also the first iPhone to support dual-band WiFi based on 2.4 GHz and 5 GHz radios, similar to the iPad. Apple claims up to 150 Mbps Wi-Fi support, which is better than the current iPad. However, this is not the full capacity of current WiFi networks. Today’s WiFi networks are based on 801.11n standards and can support in excess of 300 Mbps but it does so in increments of 75Mbps. Simply put, WiFi works by transmitting and receiving data streams in chunks of 75 Mbps using 20 MHz spectrum ‘spatial stream’. To get more than 75 Mbps, three techniques are used – these are channel bonding, spatial stream multiplexing, and radio chains.  Channel bonding is done by combining two 20 MHz streams to get 40 MHz spectrum or bandwidth of 150 Mbps. To achieve more than 150 Mbps, multiple spatial streams (up to 4 in 801.11n, but practically no more than 3) are multiplexed for up to 450 Mbps. Finally devices with multiple radios (typically 2) can chain (or multiply) this capability to achieve up to 900 Mbps on an 801.11n WiFi network.

Although Apple did not specify the details on the iPhone 5 (as Amazon did with the Fire HD), I believe the iPhone 5 has one Antenna, uses one spatial stream with two bonded channels (two 20 MHz bonded together for 40 Mhz) and one radio chain, to support up to the maximum advertised 150 Mbps of bandwidth.


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