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+\begin{itemize} + \pause + \item The telecom world loves acronyms + \pause + \item Specifications deal with functional / logical network elements + \item Cellular network contains lots of elements + \item Today, we only want to look at real-world base stations +\end{itemize} +\end{frame} + +\begin{frame}{Terminology across cellular generations} +\begin{table} +\begin{tabular}{c | c | c | c | c} + Generation & Name & Base Station & Back-haul & Next element \\ +\hline \hline + 2G & GSM/GPRS & BTS & Abis & BSC \\ + 3G & UMTS & NodeB & Iub & RNC \\ + 4G & LTE & eNodeB & S1 & MME + SGW \\ + 5G & NR & gNodeB & N2 + N3 & AMF + UPF +\end{tabular} +\end{table} +\end{frame} + +\begin{frame}{Site vs. Cell} +\begin{description} + \item[Site] A single tower and associated equipment + \begin{itemize} + \item could in theory be omnidirectional + \item in reality almost always sectorized + \item classic setup is three-sector site (120 degree per sector) + \end{itemize} + \item[Cell] A logical cell in one cellular network generation + \begin{itemize} + \item typically illuminated by one (set of) antenna + \end{itemize} +\end{description} + +\begin{itemize} + \item Result: Single site often has 9 cells + \item three sectors for each of 2G, 3G and 4G +\end{itemize} +\end{frame} + +\begin{frame}{Components of a cellular base station} +\begin{itemize} + \item Tower/Pole (civil engineering part) + \item Antenna + \item Coaxial Cable + \item Actual Base Station Electronics + \item Back-haul connection to the rest of the network + \item Power Supply / Environment (Fans, AC, UPS, ...) +\end{itemize} +\end{frame} + + +\begin{frame}{Simplified Rx/Tx chain} +\begin{itemize} + \item Simplified Receiver chain: +\digraph[scale=0.30]{rxsimple}{ + rankdir=LR; + Antenna -> Duplexer -> RF_Filter -> LNA -> Mixer -> BB_Filter -> ADC -> PHY -> L2_L3 +} + \item Simplified Transmitter chain: +\digraph[scale=0.30]{txsimple}{ + rankdir=RL; + L2_L3 -> PHY -> DAC -> BB_Filter -> Mixer -> PA -> RF_Filter -> Duplexer -> Antenna; +} +\end{itemize} + Reality is more complex in many cases (circulator, active predistortion, rx diversity, ...) +\end{frame} + + +\begin{frame}{Even more Simplified Rx/Tx chain} +\begin{itemize} + \item Simplified Receiver chain: +\digraph[scale=0.40]{rxsimple2}{ + rankdir=LR; + Antenna -> Mixer [label=RF]; + Mixer -> ADC [label="Analog Baseband"]; + ADC -> PHY [label="Digital Baseband"]; + PHY -> L2_L3 [label="Primitives"]; +} + \item Simplified Transmitter chain: +\digraph[scale=0.40]{txsimple2}{ + rankdir=RL; + L2_L3 -> PHY [label="Primitives"]; + PHY -> DAC [label="Digital Baseband"]; + DAC -> Mixer [label="Analog Baseband"]; + Mixer -> Antenna [label="RF"]; +} +\end{itemize} +\end{frame} + +\section{Evolution of Cell Sites} + +\subsection{Classic Cell Sites} + +\begin{frame}{Classic Cell Site (year 2000)} +\begin{columns} + \column{0.28\linewidth} + \centering + \includegraphics[width=36mm]{RBS2206.jpg} + \column{0.70\linewidth} + The traditional way of building cell sites: + \begin{itemize} + \item (multiple) large racks full of equipment + \item installed in [air conditioned] shelters + \item all active electronics on ground level + \item long lines of coaxial cable up the tower + \item only passive element (antenna) up tower + \item half of transmitted power lost in cable + \end{itemize} +{\tiny Image: Timur V. Voronkov via Wikimedia Commons (CC-BY-SA)} +\end{columns} +\end{frame} + +\begin{frame}{Slightly less Classic Cell Site} +\begin{columns} + \column{0.28\linewidth} + \centering + \includegraphics[width=36mm]{nokia_flexi.jpeg} + \column{0.70\linewidth} + The fist step of logical evolution: + \begin{itemize} + \item equipment becomes smaller (partial rack) + \item no strict need for large shelter anymore + \item all active electronics on ground level + \item long lines of coaxial cable up the tower + \item only passive element (antenna) up tower + \item half of transmitted power lost in cable + \end{itemize} + Equipment gets smaller, less power hungry and dissipates less heat +{\tiny Image: Peter Schmidt @33dBm} +\end{columns} +\end{frame} + +\begin{frame}{Coaxial Cables...} +Why don't we like long coaxial cables +\begin{itemize} + \item good cabling is 1/2" to 1" in diameter and costs a lot + \item installation is more like plumbing than cabling + \item looses lots of energy over length of tower; compensated by + \begin{itemize} + \item downlink: more PA; waste of energy; causs more heat dissipation + \item uplink: tower-mounted amplifier (TMA) + \end{itemize} + \item higher frequencies have even more losses (and we went from 900 MHz to 1800 MHz to 2100 MHz to 2600 MHz) + \item more bands mean more coaxial cables in parallel +\end{itemize} +\end{frame} + + +\begin{frame}{Towards Remote Radio Heads} +So why not do he logical thing and ... +\begin{itemize} + \pause + \item Generate the RF closer to the antenna? +\end{itemize} +Answer: +\begin{itemize} + \item Requires much more compact radios + \item Requires passive cooling + \item Difficult installation (heavy) + \item Environmental protection (sun, rain, temperature cycles) + \item Hard to service / replace +\end{itemize} +\end{frame} + +\subsection{(Remote) Radio Heads} + +\begin{frame}{(Remote) Radio Heads} +Solution: Instead of moving all equipment up the tower, +\begin{itemize} + \item Move only the Analog parts of the chain up + \item Transport digital samples up/down the tower + \item Base Station split in two parts: + \begin{itemize} + \item Baseband processing ({\em digital unit}) + \item Radio processing ({\em radio unit}) + \end{itemize} +\end{itemize} +\end{frame} + +\begin{frame}{Base Station split with Radio Heads} +\begin{itemize} + \item Incredibly Simplified Receiver chain: +\digraph[scale=0.30]{rxsimple2split}{ + rankdir=LR; + Antenna -> Mixer [label=RF]; + subgraph cluster_0 { + label="Radio Head"; + Mixer -> ADC [label="Analog Baseband"]; + } + ADC -> PHY [label="Digital Baseband Samples"]; + subgraph cluster_1 { + label="Baseband Unit"; + PHY -> L2_L3 [label="Primitives"]; + } +} + \item Incredibly Simplified Transmitter chain: +\digraph[scale=0.30]{txsimple2split}{ + rankdir=RL; + subgraph cluster_0 { + label="Baseband Unit"; + L2_L3 -> PHY [label="Primitives"]; + } + subgraph cluster_1 { + label="Radio Head"; + PHY -> DAC [label="Digital Baseband Samples"]; + DAC -> Mixer [label="Analog Baseband"]; + } + Mixer -> Antenna [label="RF"]; +} +\end{itemize} +\end{frame} + +\begin{frame}{Cell Sites with (Remote) Radio Heads} +\includegraphics[width=100mm]{antennas-and-rrus.jpg} +\end{frame} + +\begin{frame}{Cell Sites with (Remote) Radio Heads} +\includegraphics[width=100mm]{cellular-tower-2172041_1920.jpg} +\end{frame} + +\begin{frame}{Cell Sites with (Remote) Radio Heads} +\includegraphics[width=92mm]{lots-of-radioheads.jpeg} + +{\tiny Image: Peter Schmidt @33dBm} +\end{frame} + +\begin{frame}{New term: front-haul} +\begin{itemize} + \item {\em back-haul} is the connection between cell and core + \item {\em front-haul} is the newly-introduced term for the link between radio head and baseband unit + \item physical medium + \begin{itemize} + \item typically fiber-optic + \item copper only if radio next to baseband unit + \end{itemize} + \item physical layer + \begin{itemize} + \item OBSAI (Open Base Station Architecture Initiative) + \begin{itemize} + \item Started in 2002 by Hyundai, LG, Nokia, Samsung, ZTE + \item Mostly obsolete now + \end{itemize} + \item CPRI (Common Public Radio Interface) + \begin{itemize} + \item Ericsson, Huawei, NEC, Alcatel-Lucent + \item more adoption particularly in recent years + \end{itemize} + \item eCPRI showing up on the horizon + \end{itemize} +\end{itemize} +\end{frame} + +\begin{frame}{from fiber-based front-haul to C-RAN} +As digital baseband samples are transmitted over fiber optics +\begin{itemize} + \item can cover distances way above height of the tower + \item single-mode transceivers allow for dozens of kilometers + \item allows for cell sites without any shelter or rack + \item leads to some people proclaiming {\em cloud-RAN} or {\em centralized RAN} + \begin{itemize} + \item don't distribute baseband compute power in the field + \item bring all your baseband samples into the cloud + \item perform CPU-intensive baseband function in data center + \end{itemize} + \item bit rates are high. A single LTE 2x2 MIMO carrier at 20MHz needs 2Gbps CPRI bandwidth + \begin{itemize} + \item site with 3 sectors and multiple carriers exceeds 10Gbps + \end{itemize} + \item latency constraints are biggest limiting factor +\end{itemize} +\end{frame} + +%%\section{Antennas} + +\begin{frame}{Antennas} +\begin{itemize} + \item You learned some antenna basics + \item You think about an omnidirectional dipole + \item Almost no cellular base station antenna is like that + \item Complexity of those antennas has grown significantly +\end{itemize} +\end{frame} + +\begin{frame}{Vertical polarization vs. X-Pol} +\begin{itemize} + \item Nominally, cellular signals are emitted in vertical polarization + \item Industry has moved to two radiators at +45 / -45 degrees polarization + \item This apparently gives polarization gain, as signals reflected (by buildings) don't arrive in + vertical polarization + \item Isolation between radiators typically 20..30dB, allowing use cases like + \begin{itemize} + \item operating two transmitters without combiner + \item operating Rx + Tx without duplexer + \item diversity reception within one antenna (polarization diversity) + \end{itemize} +\end{itemize} +\end{frame} + +\begin{frame}{Single-Band vs. Multiple Bands} +\begin{itemize} + \item So you rolled out a GSM network in 900 MHz + \begin{itemize} + \item then added more GSM on 1800 MHz + \item then added 3G on 2100 MHz, ... + \end{itemize} + \item Do you add one new set of three sector antennas per band? + \begin{itemize} + \item space and weight constraints on tower + \item they may affect each others' radiation pattersn + \end{itemize} + \item Industry responds with multi-band antennas +\end{itemize} +\end{frame} + +\begin{frame}{Electrical Tilt} +\begin{itemize} + \item For RF planning, you want to determine where your cell physically ends + \item Tilting antennas downwards means RF signals emitted eventually will hit the ground + \item Adjusting the network by climing up the tower and mechanically adjusting tilt is cumbersome + \item Industry responds with {\em Electrical Tilt} + \item Rods are controlled by motors leading to {\em Remote Electrical Tilt (RET)} +\end{itemize} +\end{frame} + +\begin{frame}{MIMO} +\begin{itemize} + \item MIMO means Multiple-In / Multiple-Out + \item uses spatial diversity to establish multiple signals between different antennas + \item 2x2 MIMO is standard with LTE today + \item 5G / New Radio specified for massive MIMO (32-64 antennas in base station!) +\end{itemize} +\end{frame} + +\begin{frame}{Antennas with many ports} +\includegraphics[width=85mm]{multiport-antenna.jpg} +\end{frame} + +\begin{frame}{Where will it end?} +\includegraphics[width=115mm]{kathrein_hepta.png} +\end{frame} + +\subsection{Antenna Integrated Radio} + +\begin{frame}{Further integration} +\begin{itemize} + \item the radio head has moved up the tower + \item coaxial cables are shorter than ever + \item ... but we have more and more of them + \item So what do we do? + \pause + \item Integrate radio head inside antenna! +\end{itemize} +\end{frame} + +\begin{frame}{Antenna Integrated Radio} +\begin{columns} + \column{0.28\linewidth} + \centering + \includegraphics[width=36mm]{RAS.jpg} + \column{0.70\linewidth} + \begin{itemize} + \item Systems like {\em Nokia RAS} / {\em Ericsson AIR} + \item Radio heads completely integrated with antenna + \item no coaxial cable at all + \item CPRI over fiber directly into the antenna + \item Everything Great? New problems + \begin{itemize} + \item enormous weight not suitable everywhere + \item complicated measurements (field technicians) + \end{itemize} + \end{itemize} +\end{columns} +\end{frame} + + +\section{back-haul, hardware, software} + +\subsection{Evolution of cellular back-haul} + +\begin{frame}{Classic 2G back-haul} +\begin{itemize} + \item 2G (GSM) was specified while ISDN was hot + \item back-haul of GSM BTS is done via E1/T1 (ISDN PRI) + \item E1 has 30 usable timeslots of 64kBps each + \begin{itemize} + \item use one for signaling (A-bis RSL + OML) + \item use one quarter (16kBps) sub-slot for each voice call + \end{itemize} + \item While GSM is still deployed today, 3GPP never specified any other transport + \item Every vendor came up with their own proprietary kludge on how to carry Abis over IP +\end{itemize} +\end{frame} + +\begin{frame}{Classic 3G back-haul} +\begin{itemize} + \item 3G (UMTS) was specified when ATM was the next hot thing + \item back-haul of eNodeB is done via ATM + \item in reality, often Inverse ATM Multiplex (ATM over 4xE1 ISDN) + \item 3GPP at least later adapted specs for IP based transport + \begin{itemize} + \item Every 20ms voice codec frame split over three different UDP packets. yay! + \end{itemize} +\end{itemize} +\end{frame} + +\begin{frame}{4G back-haul} +\begin{itemize} + \item 4G is first 3GPP cellular technology transported over IP from day one + \item Therefore, no exotic physical layers + \item Ethernet in most cases + \item Problem: Where do we get clock from? + \begin{itemize} + \item ISDN/E1/ATM always provided clock reference + \item Ethernet doesn't provide clock reference + \end{itemize} +\end{itemize} +\end{frame} + +\begin{frame}{IP-based back-haul and base station clocking} +\begin{itemize} + \item cellular base stations need super stable clock reference + \begin{itemize} + \item requirement of 30 ppb is almost 1000 times more accurate than crystal + \item even ovenized crystals (OCXOs) not long-term stable enough + \end{itemize} + \item in the post-ISDN/PDH/SDH days, pick your poison: + \begin{itemize} + \item go for a GPS-DO and create a single point of failure, or + \item use Synchronous Ethernet and loose the advantage of low-cost COTS Ethernet Switches, or + \item use IEEE PTP and hope your switches don't introduce too much jitter, or + \item let your base stations hammer your NTP server and pray + \end{itemize} +\end{itemize} +\end{frame} + +\subsection{Base Station Electronics} + +\begin{frame}{Base Station Electronics: Baseband} +\begin{itemize} + \item Typically some multi-core DSP + \begin{itemize} + \item e.g. TI Keystone2 (eight 64bit 1.2GHz DSPs) + \item built-in coprocessors (FFT, crypto, Turbo Decoder, Viterbi) + \item built-in CPRI/OBSAI Controller + \item four ARM Cortex A-15 for L2/L3 processing + \end{itemize} + \item Often also FPGAs + vendor-specific ASICs + \begin{itemize} + \item Ericsson big on ASICs + \item proprietary ASICs/SoCs with 10.5 billion transistors + \item that's comparable to Apple A12X / Huawei Kirin 990! + \end{itemize} +\end{itemize} +\end{frame} + +\begin{frame}{Base Station Electronics: Radiohead} +\begin{itemize} + \item Some RFIC (typically ADI) + \begin{itemize} + \item ADC + DAC + \item up/downconversion (mixer) + \item on-chip filters + \end{itemize} + \item Power Amplifier + \begin{itemize} + \item typically 2 stages of drivers + final PA + \end{itemize} + \item Circulator + \begin{itemize} + \item protect PA from power reflected back from antenna + \end{itemize} + \item Cavity Duplexer + \item [Digital] [Adaptive] Pre-distortion + \begin{itemize} + \item Ensure Linear PA even for high-PAPR signals + \end{itemize} +\end{itemize} +\end{frame} + + +\subsection{Base Station Software} + +\begin{frame}{Base Station Software} +\begin{itemize} + \item Don't expect too many familiar things here + \item decades of proprietary development by large corporations + \item Enea OSE (Operating System Embedded) popular with Ericsson + Nokia + \begin{itemize} + \item proprietary microkernel with custom-everything including filesystems + \end{itemize} + \item vxworks found in some equipment like Huawei radioheads + \item Linux found mostly only in small cells, inheriting software from femtocells +\end{itemize} +\end{frame} + +\begin{frame}{Further Reading} +\begin{itemize} + \item \url{http://cpri.info/} + \item FlexiWCDMA teardown: \url{https://www.youtube.com/watch?v=d5xT4p9FXIw} + \item Ericsson RBS600 teardown: \url{https://www.youtube.com/watch?v=qO127zY3voE} +\end{itemize} +\end{frame} + +\begin{frame}{Thanks} +Thanks for your attention. + + You have a General Public License to ask questions now :) +\end{frame} + +\end{document} diff --git a/2019/cccb-cellular_base_station_technology/gsm-tower.jpg b/2019/cccb-cellular_base_station_technology/gsm-tower.jpg Binary files differnew file mode 100644 index 0000000..7040c1b --- /dev/null +++ b/2019/cccb-cellular_base_station_technology/gsm-tower.jpg diff --git a/2019/cccb-cellular_base_station_technology/kathrein_hepta.png b/2019/cccb-cellular_base_station_technology/kathrein_hepta.png Binary files differnew file mode 100644 index 0000000..cd0203c --- /dev/null +++ b/2019/cccb-cellular_base_station_technology/kathrein_hepta.png diff --git a/2019/cccb-cellular_base_station_technology/lots-of-radioheads.jpeg b/2019/cccb-cellular_base_station_technology/lots-of-radioheads.jpeg Binary files differnew file mode 100644 index 0000000..a704f6b --- /dev/null +++ b/2019/cccb-cellular_base_station_technology/lots-of-radioheads.jpeg diff --git a/2019/cccb-cellular_base_station_technology/multiport-antenna.jpg b/2019/cccb-cellular_base_station_technology/multiport-antenna.jpg Binary files differnew file mode 100644 index 0000000..1448fa2 --- /dev/null +++ b/2019/cccb-cellular_base_station_technology/multiport-antenna.jpg diff --git a/2019/cccb-cellular_base_station_technology/nokia_flexi.jpeg b/2019/cccb-cellular_base_station_technology/nokia_flexi.jpeg Binary files differnew file mode 100644 index 0000000..4c79bd4 --- /dev/null +++ b/2019/cccb-cellular_base_station_technology/nokia_flexi.jpeg diff --git a/2019/cccb-cellular_base_station_technology/nokia_flexi2.jpeg b/2019/cccb-cellular_base_station_technology/nokia_flexi2.jpeg Binary files differnew file mode 100644 index 0000000..3d5805b --- /dev/null +++ b/2019/cccb-cellular_base_station_technology/nokia_flexi2.jpeg diff --git a/2019/cccb-cellular_base_station_technology/old_rack.jpeg b/2019/cccb-cellular_base_station_technology/old_rack.jpeg Binary files differnew file mode 100644 index 0000000..b5062e0 --- /dev/null +++ b/2019/cccb-cellular_base_station_technology/old_rack.jpeg diff --git a/2019/cccb-cellular_base_station_technology/working-on-cell-tower-3850689_1920.jpg b/2019/cccb-cellular_base_station_technology/working-on-cell-tower-3850689_1920.jpg Binary files differnew file mode 100644 index 0000000..e2d7977 --- /dev/null +++ b/2019/cccb-cellular_base_station_technology/working-on-cell-tower-3850689_1920.jpg |
