Home | Reports | Technical Documents | Tech-Blog | One-Shot Gallery | Korea ICT News | Korea Communication Market Data | List of Contributors | Become a Contributor |    
 
 
Section 5G 4G LTE C-RAN/Fronthaul Gigabit Internet IPTV/Video Streaming IoT SDN/NFV Wi-Fi KT SK Telecom LG U+ Network Protocol Samsung   Korean Vendors
 
Real World Private 5G Cases   4 Deployment Models On-Premise Cases 5G Core Control Plane Sharing Cases

5G Core Sharing Cases

   
 
Private 5G Deployment   • Private 5G Frequency Allocation Status in Korea  South Korean government's regulations on private 5G and KT's strategy for entering the market
Cases in Korea   Private 5G Operators |   SK Networks Service (SI) Sejong Telecom (Wire-line Carrier) KT MOS (Affiliate of KT) • Newgens (SI) • NAVER Cloud more >>  
    Enterprise DIY |   Korea Hydro & Nuclear Power (Power Plant) Korea Electric Power Corporation (Energy) • Republic of Korea Navy more >>
 
CHANNELS     HFR Private 5G Solution (my5G)       my5G Solution Components       my5G Key Features        my5G Resources        my5G News          
 
banner
banner
Why no Soft Handover in LTE ?
December 20, 2016 | By Mohamed Abdel Monem @ Vodafone
Online viewer:
Comments (3)
14

We are pleased to share with you all an interesting article contributed by Mohamed Abdel Monem. 

 
 

Mohamed Abdel Monem 

Radio Optimization Senior Engineer at Vodafone Egypt

 

 

All Articles by Mohamed Abdel Monem  

 
     
  How to contribute your article to Netmanias.com !  
     
  List of Contributors  

 

 

     
 

When LTE system was developed one of the big technical feature from UMTS Soft/Softer handover was missing from the architecture. There are many specific reasons why LTE dropped altogether soft handover (connect-before-break) from the system design.

 

Before discussing about why LTE skipped soft handover and only implemented hard handover, let’s check the basic concept of soft/softer handover.

 

 

Soft handover concept

 

Soft handover or connect-before-break handover is a category of handover procedure where radio links are added or removed in such a fashion that there is always one radio link connected to the UE.

 

All the radio links connected to the UE at a particular time are part of the ACTIVE SET and the number can vary from 1 to 8. This means at least one and maximum of 8 radio links are connected to the UE.

 

Soft handover is a part of WCDMA system which is basically same in concept as in CDMA systems.

 

In the case of soft handover the mobile station is in the overlapping cell coverage area of two sectors belonging to different base stations. In downlink direction signals received from different base stations are combined at the rake receiver of the UE. In the uplink the scrambled signals from different base stations for a particular UE are compared frame-by-frame basis at the RNC and the best candidate is selected after each interleaving period; i.e. every 10, 20, 40 or 80ms.

 

Soft and softer handovers are only possible when UE is in connected state with dedicated channel (DCH).

 

Even with HSDSCH (High-Speed Downlink Shared Channel) there is no soft handover in UMTS. In cased HSDPA communication there is only hard handover which is break before connect. Means UE is never connected to more than one radio link at a time and when UE goes out of coverage of a particular cell that radio link is teared down before adding the better radio link.

 

 

Requirements for soft handover and what is missing in LTE

 

Let’s discuss why LTE does not have soft handover as in WCDMA and CDMA systems. Though there are various reasons, I documented here three causes why soft handover was omitted from LTE.

 

Adjacent Cell Frequency Reuse

 

Soft handover is possible in CDMA because adjacent cells can operate on the same frequencies as long as they use different scrambling codes. So, a UE can listen to two different cells by decoding the received signals twice, using a scrambling code from each cell on each for each decoded signal. This allows a UE to communicate with both cells during handover, making it a soft handover.

 

LTE is based on OFDMA, which is fundamentally a frequency division method. This means that a UE has to actually resync to a different set of frequency subcarriers when it hands over between cells, removing the possibility for soft handover. In fact, when a handover is beginning, an LTE UE has to go into a ‘compressed mode’ where it listens to its current cell for part of the time and searches for a new cell the rest of the time. With modern radio technology, this retuning can happen fast enough to make the inter-frequency retuning much more seamless than it was in older technologies like GSM, obviating the need for soft handover.

 

Flat Architecture

 

LTE  has flat architecture which means there’s no central node controller like the BSC or RNC. Therefore there’s no need to sum up multiple active signals like you would say for in cdma. Another reason being, there’s no need for power control in LTE because of its orthogonal  modulation scheme, there’s no self interference (like in cdma) so no worries about Rx diversity gain and therefore SHO can be dropped.

 

Orthogonality in LTE

 

Cell-edge reception (which was at the core of Soft HO design in WCDMA) issue is not quite applicable in LTE networks because of orthogonality in both uplink and downlink. Therefore soft handover can be dropped from the LTE system.

 

 

Conclusion

 

Though LTE does not have soft or softer handover it still maintains seamless mobility using hard handover. In LTE there are three different types of handover can be possible

  • Intra-LTE Handover: In this case source and target cells are part of the same LTE network.
  • Inter-LTE Handover: Handover happens towards other LTE nodes. (Inter-MME and Inter-SGW)
  • Inter-RAT Handover: Handover between different radio technologies. For example handover from LTE to WCDMA.

 

 
     

 

 

Khan 2016-12-21 18:49:23

THanks Maker. It is useful. 

Item No.1 and No.2 are totally easy and clear to understand. But item No.3, it seems so complicated.

jfer3351 2017-01-09 23:23:03

Thanks, Mohamed.

As stated by the previous reader, could you please elaborate on the third cause ("orthogonality in LTE")?

I might be missing something, but I fail to see the connection between UL/DL orthogonality and soft handover... What do you exactly mean by "UL/DL orthogonality"? Why is this relevant to the lack of soft handover?

Thanks.-

JackLin 2019-04-24 21:26:07

Hi Mohamed, I think you should state the reference of this article: http://www.3glteinfo.com/soft-handover-lte/

Thank you for visiting Netmanias! Please leave your comment if you have a question or suggestion.
Related Contents
12/22/2017
Netmanias Blog
11/17/2017
Netmanias Blog
08/04/2017
Netmanias Blog
07/28/2017
Netmanias Blog
12/29/2016
Netmanias Blog
04/08/2014
Netmanias Technical Documents
03/21/2014
Netmanias Technical Documents
10/22/2013
Netmanias Technical Documents
 
 
 
 

[HFR Private 5G: my5G]

 

Details >>

 

 

 

     
         
     

 

     
     

Subscribe FREE >>

Currently, 55,000+ subscribed to Netmanias.

  • You can get Netmanias Newsletter

  • You can view all netmanias' contents

  • You can download all netmanias'

    contents in pdf file

     
     

 

     
         
     

 

 

 

View All (854)
4.5G (1) 5G (101) AI (7) AR (1) ARP (3) AT&T (1) Akamai (1) Authentication (5) BSS (1) Big Data (2) Billing (1) Blockchain (3) C-RAN/Fronthaul (18) CDN (4) CPRI (4) Carrier Ethernet (3) Charging (1) China (1) China Mobile (2) Cisco (1) Cloud (5) CoMP (6) Connected Car (4) DHCP (5) EDGE (1) Edge Computing (1) Ericsson (2) FTTH (6) GSLB (1) GiGAtopia (2) Gigabit Internet (19) Google (7) Google Global Cache (3) HLS (5) HSDPA (2) HTTP Adaptive Streaming (5) Handover (1) Huawei (1) IEEE 802.1 (1) IP Routing (7) IPTV (21) IoST (3) IoT (56) KT (43) Korea (20) Korea ICT Market (1) Korea ICT Service (13) Korea ICT Vendor (1) LG U+ (18) LSC (1) LTE (78) LTE-A (16) LTE-B (1) LTE-H (2) LTE-M (3) LTE-U (4) LoRa (7) MEC (4) MPLS (2) MPTCP (3) MWC 2015 (8) NB-IoT (6) Netflix (2) Network Protocol (21) Network Slice (1) Network Slicing (4) New Radio (9) Nokia (1) OSPF (2) OTT (3) PCRF (1) Platform (2) Private 5G (10) QoS (3) RCS (4) Roaming (1) SD-WAN (17) SDN/NFV (71) SIM (1) SK Broadband (2) SK Telecom (35) Samsung (5) Security (16) Self-Driving (1) Small Cell (2) Spectrum Sharing (2) Switching (6) TAU (2) UHD (5) VR (2) Video Streaming (12) VoLTE (8) VoWiFi (2) Wi-Fi (31) YouTube (6) blockchain (1) eICIC (1) eMBMS (1) iBeacon (1) security (1) telecoin (1) uCPE (2)
Password confirmation
Please enter your registered comment password.
Password