With an ever increasing demand for RF spectrum, the wireless industry will have to break paradigms to achieve what once was only a supposition. Two very important challenges for the future of wireless communications are spectral efficiency and energy efficiency. Some strategies are currently under study to meet the challenge. One of them is to drastically increase the number of transceivers of the wireless nodes, an approach referred to as “massive MIMO”.
Data interface requirements
As Nutaq described in a comprehensive six-post blog series, using very large scale antenna arrays with many transceivers (hundreds) on a base station, could be a solution. However a gap between theory and practice still remains, and such a huge system involves many engineering challenges.
As Nutaq thoroughly explained in a previous post, using many transceivers to cover a large bandwidth results in very high data rates within the system. To make the situation even more difficult, all the data must be routed to a central processing unit for the massive MIMO baseband processing. Simple calculations indicate an approximately 126 Gbps requirement for the particular case of a 128-transceiver system covering a 20 MHz bandwidth (calculations have been made assuming 16-bit digital sampling at a 30.72 MHz sampling rate for both I and Q samples). Most data interfaces are not suited to support this kind of throughput. This blog post reviews the different options and explains what is required on a technical basis to enable their application.
Table 1 shows the expected throughputs for different data interfaces. Figure 1 shows the limitation of each interface as the number of channels grows (transceivers).
|Interface||Latency||Typical rate (Mbps)|
|PCIe gen1 x4||μ sec||6400|
|PCIe gen2 x8||μ sec||28800|
|1 Gigibit Ethernet||m sec||896|
|10 Gigibit Ethernet||m sec||9000|